CHAPTER X

METEOROLOGICAL RECORDS FROM THE PERUVIAN ANDES

INTRODUCTION

The data in this chapter, on the weather and climate of the Peruvian Andes, were gathered under the usual difficulties that accompany the collection of records at camps scarcely ever pitched at the same elevation or with the same exposure two days in succession. Some of them, and I may add, the best, were contributed by volunteer observers at fixed stations. The observations are not confined to the field of the Yale Peruvian Expedition of 1911, but include also observations from Professor Hiram Bingham’s Expeditions of 1912 and 1914-15, together with data from the Yale South American Expedition of 1907. In addition I have used observations supplied by the Morococha Mining Company through J. P. Little. Some hitherto unpublished observations from Cochabamba, Bolivia, gathered by Herr Krüger at considerable expense of money for instruments and of time from a large business, are also included, and he deserves the more credit for his generous gift of these data since they were collected for scientific purposes only and not in connection with enterprises in which they might be of pecuniary value. My only excuse to Herr Krüger for this long delay in publication (they were put into my hands in 1907) is that I have wanted to publish his data in a dignified form and also to use them for comparison with the data of other climatic provinces.

A further word to the reader seems necessary before he examines the following curves and tables. It would be somewhat audacious to assume that these short-term records have far-reaching importance. Much of their value lies in their organization with respect to the data already published on the climate of Peru. But since this would require a delay of several years in their publication it seems better to present them now in their simplest form. After all, the professional climatologist, to whom they are chiefly of interest, scarcely needs to have such organization supplied to him. Then, too, we hope that there will become available in the next ten or fifteen years a vastly larger body of climatological facts from this region. When these have been collected we may look forward to a volume or a series of volumes on the “Climate of Peru,” with full statistical tables and a complete discussion of them. That would seem to be the best time for the reproduction of the detailed statistics now on hand. It is only necessary that there shall be sufficient analysis of the data from time to time to give a general idea of their character and to indicate in what way the scope of the observations might profitably be extended. I have, therefore, taken from the available facts only such as seem to me of the most importance because of their unusual character or their special relations to the boundaries of plant provinces or of the so-called “natural regions” of geography.

MACHU PICCHU[27]

The following observations are of special interest in that they illustrate the weather during the southern winter and spring at the famous ruins of Machu Picchu in the Canyon of Torontoy. The elevation is 8,500 feet. The period they cover is too short to give more than a hint of the climate or of the weather for the year. It extends from August 20, 1912, to November 6, 1912 (79 days).

ANALYTICAL TABLE OF WIND DIRECTIONS, MACHU PICCHU, 1912

-----------+--------------------------------------------------------+ | Number of Observations | Direction +----------------------------+---------------------------| of wind | Aug. 20 -- Sept. 30 | Oct. 1 -- Nov. 6 | | 7 a. m. 1 p. m. 7 p. m. | 7 a. m. 1 p. m. 7 p. m. | -----------+----------------------------+---------------------------+ N. | 5 2 5 | 2 -- -- | N.W. | 9 10 14 | 4 6 11 | W. | -- 1 2 | 2 2 4 | S. W. | -- -- 1 | 1 1 6 | S. | -- -- 1 | -- -- 2 | S. E. | 4 2 1 | -- -- 3 | E. | 6 3 3 | 12 4 4 | N. E. | 8 7 6 | 4 1 3 | CALM | -- -- 2 | 5 3 3 | -----------+----------------------------+---------------------------+

----------------------------------------------------------------+ | Percentages of Total Observation[28] | Direction|------------------------------------------------------| of wind | Aug. 20 ---- Sept. 30 | Oct. 1 ---- Nov. 6 | | 7 a. m. 1 p.m. 7 p. m. | 7 a. m. 1 p. m. 7 p. m.| ----------------------------------------------------------------| N. | 15.6 8.0 14.2 | 6.7 ---- ---- | N. W. | 28.1 40.0 40.0 | 13.3 35.3 30.7 | W. | ---- 4.0 5.7 | 6.7 11.8 11.1 | S. W. | ---- ---- 2.8 | 3.3 5.9 16.7 | S. | ---- ---- 2.8 | ---- ---- 5.5 | S. E. | 12.5 8.0 2.8 | ---- ---- 8.3 | E. | 18.8 12.0 8.6 | 40.0 23.5 11.1 | N. E. | 25.0 28.0 17.1 | 13.3 5.9 8.3 | CALM | ---- ---- 5.7 | 16.7 17.6 8.3 | ----------------------------------------------------------------+

The high percentage of northwest winds during afternoon hours is due to the up-valley movement of the air common to almost all mountain borders. The air over a mountain slope is heated more than the free air at the same elevation over the plains (or lower valley); hence a barometric gradient towards the mountain becomes established. At Machu Picchu the Canyon of Torontoy trends northwest, making there a sharp turn from an equally sharp northeast bend directly upstream. The easterly components are unrelated to the topography. They represent the trades. If a wind rose were made for still earlier morning hours these winds would be more faithfully represented. That an easterly and northeasterly rather than a southeasterly direction should be assumed by the trades is not difficult to believe when we consider the trend of the Cordillera--southeast to northwest. The observations from here down to the plains all show that there is a distinct change in wind direction in sympathy with the larger features of the topography, especially the deep valleys and canyons, the trades coming in from the northeast.

CLOUDINESS

It will be seen that the sky was overcast or a fog lay in the valley 53 per cent of the time at early morning hours. Even at noon the sky was at no time clear, and it was more than 50 per cent clear only 18 per cent of the time. Yet this is the so-called “dry” season of the valleys of the eastern Andes. The rainfall record is in close sympathy. In the 79 days’ observations rain is recorded on 50 days with a greater proportion from mid-September to the end of the period (November 6), a distinct transition toward the wet period that extends from December to May. The approximate distribution of the rains by hours of observation (7 A. M., 1 P. M., 7 P. M.) was in the ratio 4:3:6. Also the greatest number of heavy showers as well as the greatest number of showers took place in the evening. The rainfall was apparently unrelated to wind direction in the immediate locality, though undoubtedly associated with the regional movement of the moist plains air toward the mountains. All these facts regarding clouds and rain plainly show the location of the place in the belt of maximum precipitation. There is, therefore, a heavy cover of vegetation. While the situation is admirable for defence, the murky skies and frequent fogs somewhat offset its topographic surroundings as a lookout.

ANALYTICAL TABLE OF THE STATE OF THE SKY, MACHU PICCHU, 1912

---------------+-------------+-------------+ | Morning | Total | ---------------+------+------+------+------+ |Aug.- |Oct.- |Days | % | |Sept. |Nov. | | | ---------------+------+------+------+------+ Foggy | 3.0 | 14.0 | 17.0 | 28.4 | Overcast | 12.0 | 3.0 | 15.0 | 25.0 | 50-100% cloudy | 4.0 | 10.0 | 14.0 | 23.3 | 0-50% cloudy | 6.0 | 4.0 | 10.0 | 16.7 | Clear | 3.0 | 1.0 | 4.0 | 6.6 | ---------------+------+------+------+------+

---------------+-------------+-------------+ | Noon | Total | ---------------+------+------+------+------+ |Aug.- |Oct.- | Days | % | |Sept. |Nov. | | | ---------------+------+------+------+------+ Foggy | 1.0 | -- | 1.0 | 2.6 | Overcast | 6.0 | 8.0 | 14.0 | 36.8 | 50-100% cloudy | 0.0 | 7.0 | 16.0 | 42.2 | 0-50% cloudy | 5.0 | 2.0 | 7.0 | 18.4 | Clear | 0.0 | 0.0 | 0.0 | 0.0 | ---------------+------+------+------+------+

---------------+-------------+------------- | Evening | Total ---------------+------+------+------+------ |Aug.- |Oct.- |Days | % |Sept. |Nov. | | ---------------+------+------+------+------ Foggy | 1.0 | 2.0 | 3.0 | 4.3 Overcast | 13.0 | 11.0 | 24.0 | 34.8 50-100% cloudy | 8.0 | 15.0 | 23.0 | 33.3 0-50% cloudy | 9.0 | 4.0 | 13.0 | 18.8 Clear | 3.0 | 3.0 | 6.0 | 8.8 ---------------+------+------+------+------

SANTA LUCIA[29]

Santa Lucia is a mining center in the province of Puno (16° S.), at the head of a valley here running northeast towards Lake Titicaca. Its elevation, 15,500 feet above sea level, confers on it unusual interest as a meteorological station. A thermograph has been installed which enables a closer study of the temperature to be made than in the case of the other stations. It is unfortunate, however, that the observations upon clouds, wind directions, etc., should not have been taken at regular hours. The time ranges from 8.30 to 11.30 for morning hours and from 2.30 to 5.30 for afternoon. The observations cover portions of the years 1913 and 1914.

TEMPERATURE

Perhaps the most striking features of the weather of Santa Lucia are the highly regular changes of temperature from night to day or the uniformly great diurnal range and the small differences of temperature from day to day or the low diurnal variability. For the whole period of nearly a year the diurnal variability never exceeds 9.5° F. (5.3° C.) and for days at a time it does not exceed 2-3° F. (1.1°-1.7° C.). The most frequent variation, occurring on 71 per cent of the total number of days, is from 0-3° F., and the mean for the year gives the low variability of 1.9° F. (1.06° C.). These facts, illustrative of a type of weather comparable in _uniformity_ with low stations on the Amazon plains, are shown in the table following as well as in the accompanying curves.

FREQUENCY OF THE DIURNAL VARIABILITY, SANTA LUCIA, 1913-14

----------+----+----+----+----+-----+ | | | | | | Degrees F.|May |June|July|Aug.|Sept.| ----------+----+----+----+----+-----+ 0 | -- | 2 | 6 | 3 | 4 | 0-1 | 2 | 7 | 7 | 5 | 6 | 1-2 | 11 | 5 | 7 | 11 | 7 | 2-3 | 2 | 8 | 8 | 9 | 3 | 3-4 | 4 | 4 | 2 | 1 | 4 | 4-5 | 1 | 3 | 1 | -- | 2 | Over 5 | -- | 1 | -- | 2 | 4 | ----------+----+----+----+----+-----+ Days per| 20 | 30 | 31 | 31 | 30 | month| | | | | | ----------+----+----+----+----+-----+

----------+----+----+----+----+----+-----++--------- | | | | | | ||Total No. Degrees F.|Oct.|Nov.|Dec.|Jan.|Feb.|March||of days ----------+----+----+----+----+----+-----++--------- 0 | 6 | 2 | -- | 1 | -- | 2 || 26 0-1 | 4 | 8 | 12 | 14 | 9 | 5 || 79 1-2 | 8 | 5 | 5 | 4 | 9 | 13 || 85 2-3 | 7 | 7 | 5 | 5 | 4 | 6 || 64 3-4 | 1 | 3 | 6 | 2 | 4 | 2 || 33 4-5 | 1 | 3 | -- | 2 | 1 | 1 || 15 Over 5 | 4 | 2 | 2 | 3 | 1 | -- || 19 ----------+----+----+----+----+----+-----++--------- Days per| 31 | 30 | 30 | 31 | 28 | 29 || 321 month| | | | | | || ----------+----+----+----+----+----+-----++---------

If we take the means of the diurnal variations by months we have a still more striking curve showing how little change there is between successive days. June and December are marked by humps in the curve. They are the months of extreme weather when for several weeks the temperatures drop to their lowest or climb to their highest levels. Moreover, there is at these lofty stations no pronounced lag of the maximum and minimum temperatures for the year behind the times of greatest and least heating such as we have at lower levels in the temperate zone. Thus we have the highest temperature for the year on December 2, 70.4° F. (21.3° C.), the lowest on June 3, 0.2° F. (--17.7° C.). The daily maxima and minima have the same characteristic. Radiation is active in the thin air of high stations and there is a very direct relation between the times of greatest heat received and greatest heat contained. The process is seen at its best immediately after the sun is obscured by clouds. In five minutes I have observed the temperature drop 20° F. (11.1° C.) at 16,000 feet (4,877 m.); and a drop of 10° F. (5.6° C.) is common anywhere above 14,000 feet (4,267 m.). In the curves of daily maximum and minimum temperatures we have clearly brought out the uniformity with which the maxima of high-level stations rise to a mean level during the winter months (May-August). Only at long intervals is there a short series of cloudy days when the maximum is 10°-12° F. (5.6°-6.7° C.) below the normal and the minimum stands at abnormally high levels. Since clouds form at night in quite variable amounts--in contrast to the nearly cloudless days--there is a far greater variability among the minimum temperatures. Indeed the variability of the winter minima is greater than that of the summer minima, for at the latter season the nightly cloud cover imposes much more stable atmospheric temperatures. The summer maxima have a greater degree of variability. Several clear days in succession allow the temperature to rise from 5°-10° F. (2.8°-5.6° C.) above the winter maxima. But such extremes are rather strictly confined to the height of the summer season--December and January. For the rest of the summer the maxima rise only a few degrees above those of the winter. This feature of the climate combines with a December maximum of rainfall to limit the period of most rapid plant growth to two months. Barley sown in late November could scarcely mature by the end of January, even if growing on the Argentine plains and much less at an elevation which carries the night temperatures below freezing at least once a week and where the mean temperature hovers about 47° F. (8.3° C.). The proper conditions for barley growing are not encountered above 13,000 to 13,500 feet and the farmer cannot be certain that it will ripen above 12,500 feet in the latitude of Santa Lucia.

The curve of mean monthly temperatures expresses a fact of great importance in the plant growth at high situations in the Andes--the sharp break between the winter and summer seasons. There are no real spring and autumn seasons. This is especially well shown in the curve for non-periodic mean monthly range of temperature for the month of October. During the half of the year that the sun is in the southern hemisphere the sun’s noonday rays strike Santa Lucia at an angle that varies between 0° and 16° from the vertical. The days and nights are of almost equal length and though there is rapid radiation at night there is also rapid insolation by day. When the sun is in the northern hemisphere the days are shortened from one to two hours and the angle of insolation decreased, whence the total amount of heat received is so diminished that the mean monthly temperature lies only a little above freezing point. In winter the quiet pools beside the springs freeze over long before dark as the hill shadows grow down into the high-level valleys, and by morning ice also covers the brooks and marshes. Yet the sun and wind-cured _ichu_ grass lives here, pale green in summer, straw-yellow in winter. The tola bush also grows rather abundantly. But we are almost at the upper limit of the finer grasses and a few hundred feet higher carries one into the realm of the snowline vegetation, mosses and lichens and a few sturdy flowering plants.

For convenience in future comparative studies the absolute extremes are arranged in the following table:

ABSOLUTE MONTHLY EXTREMES, SANTA LUCIA, 1913-14

-----------------------+----------++----------+---------------- Date | Highest || Lowest | Date -----------------------+----------++----------+---------------- May[30] (12) | 62° F. || 9° F. | May (25, 26) June (4 days) | 60° F. || 0.2° F. | June (3) July (4 days, 31) | 60° F. || 5° F. | July (8) Aug. (8, 26) | 62° F. || 4° F. | Aug. (4, 5) Sept. (several days) | 62° F. || 7° F. | Sept. (4 days) Oct. (24) | 63° F. || 10° F. | Oct. (12, 13) Nov. (11)[31] | 63° F. || 24.0° F. | Nov. (29) Dec. (2) | 70.4° F. || 22.2° F. | Dec. (14) Jan. (19) | 69.5° F. || 26.5° F. | Jan. (3, 15) Feb. (16, 18) | 63.2° F. || 30.5° F. | Feb. (23) March (8) | 68.4° F. || 28.5° F. | March (6) -----------------------+----------++----------+----------------

RAINFALL

The rainfall record for Santa Lucia is for the year beginning November, 1913. For this period the precipitation amounts to 24.9 inches of which over 85 per cent fell in the rainy season from November to March. Most of the rain fell during the violent afternoon tempests that characterize the summer of these high altitudes.

The rainfall of Santa Lucia for this first year of record approximates closely to the yearly mean of 23.8 inches for the station of Caylloma in the adjacent province of that name. Caylloma is the center of a mining district essentially similar to Santa Lucia though the elevation of its meteorological station, 14,196 feet (4,330 m.), is lower. It is one of the few Peruvian stations for which a comparatively long series of records is available. The _Boletín de la Sociedad Geográfica de Lima_[32] contains a résumé of rainfall and temperature for seven years, 1896-7 to 1902-3. Later data may be found in subsequent volumes of the same publication but they have not been summarized or in any way prepared for analysis and they contain several typographical errors. A graphic representation of the monthly rainfall for the earlier period is here reproduced from the _Boletín de minas del Perú_.[33] The amount of precipitation fluctuates considerably from year to year. For the earlier period, with a mean of 23.8 inches the minimum (1896-7) was 8 inches and the maximum (1898-9) 36 inches. For the later period, 1903-4 to 1910-11, with a mean of 29.5 inches the minimum (1904-5) was 17.5 inches and the maximum (1906-7) was 43 inches.

RAINFALL, SANTA LUCIA, NOV. 1913 TO OCT. 1914

---------+---------+----------+----------+--------------- |No of |No. of |Max. for |Total rainfall |fine days|rainy days|single day|in inches ---------+---------+----------+----------+--------------- November | 9 | 21 | 1.150 | 4.264[34] December | 16 | 15 | .700 | 6.439 January | 17 | 14 | .610 | 3.313 February | 9 | 17 | .910 | 2.975 March | 11 | 20 | 1.102 | 4.381 April | 17 | 13 | 0.31 | 0.92 May | 8 | 23 | 0.35 | 1.63 June | 27 | 3 | 0.05 | 0.07 July | 31 | 0 | 0.00 | 0.00 August | 31 | 0 | 0.00 | 0.00 September| 23 | 7 | 0.05 | 0.35 October | 21 | 10 | 0.14 | 0.56 ---------+---------+----------+----------+--------------- Total | | | | 24.902 ---------+---------+----------+----------+---------------

WIND

An analysis of the wind at Santa Lucia shows an excess of north and south winds over those of all other directions. The wind-rose for the entire period of observation (Fig. 104) clearly expresses this fact. When this element is removed we observe a strongly seasonal distribution of the wind. The winter is the time of north and south winds. In summer the winds are chiefly from the northeast or the southwest. Among single months, August and February show this fact clearly as well as the less decisive character of the summer (February) wind.

The mean wind velocity for the month of February was 540 meters per minute for the morning and 470 meters per minute for the afternoon. The higher morning rate, an unusual feature of the weather of high stations, or indeed of wind-phenomena in general, is due, however, to exceptional changes in wind strength on two days of the month, the 16th and 25th, when the velocity decreased from a little less than a thousand meters per minute in the morning to 4 and 152 meters respectively in the afternoon. More typical is the March record for 1914 at Santa Lucia, when the wind was _always_ stronger in the afternoon than in the morning, their ratios being 550 to 510.

CLOUD

The greater strength of the afternoon wind would lead us to suppose that the cloudiness, which in the trade-wind belt, is to so great an extent dependent on the wind, is greatest in the afternoon. The diagrams bring out this fact. Barely is the sky quite clear after the noon hour. Still more striking is the contrast between the morning and afternoon if we combine the two densest shadings of the figures. Light, high-lying cirrus clouds are most characteristic of early morning hours. They produce some very striking sky effects just before sunrise as they catch the sun’s rays aloft. An hour or two after sunrise they disappear and small cumulus clouds begin to form. These grow rapidly as the winds begin and by afternoon become bulky and numerous. In the wet season they grow into the nimbus and stratus types that precede a sudden downpour of water or a furious hailstorm. This is best seen from the base of a mountain range looking towards the crest, where the cloud-and rain-making processes of this type are most active.

CLOUD ANALYSIS, SANTA LUCIA

--------------+---------+---------+---------+---------+---------++---------+ | Nov. | Dec. | Jan. | Feb. | March || Total | Type of cloud |a.m. p.m.|a.m. p.m.|a.m. p.m.|a.m. p.m.|a.m. p.m.||a.m. p.m.| --------------+---------+---------+---------+---------+---------++---------+ Cirrus | 6 2 | 15 2 | 9 2 | 5 3 | 6 3 || 41 12 | Cirro-stratus | -- -- | -- -- | -- -- | -- -- | -- -- || -- -- | Cirro-cumulus | 4 4 | 7 11 | 3 5 | 6 8 | 17 10 || 37 38 | Cumulus | 3 4 | 4 7 | 10 9 | 15 13 | 5 13 || 37 46 | Strato-cumulus| 2 6 | 3 10 | 7 14 | 2 3 | -- 3 || 14 36 | Stratus | -- -- | -- 1 | -- -- | -- 1 | 1 2 || 2 4 | Nimbus | -- -- | -- -- | -- -- | -- -- | -- -- || -- -- | Clear | -- -- | 2 -- | 2 1 | -- -- | 2 -- || 6 1 | --------------+---------+---------+---------+---------+---------++---------+

UNUSUAL WEATHER PHENOMENA, SANTA LUCIA, 1913-14

The following abstracts are selected because they give some important features of the weather not included in the preceding tables and graphs. Of special interest are the strong contrasts between the comparatively high temperatures of midday and the sudden “tempests” accompanied by rain or hail that follow the strong convectional movements dependent upon rapid and unequal heating. The furious winds drive the particles of hail like shot. It is sometimes impossible to face them and the pack train must be halted until the storm has passed. Frequently they leave the ground white with hailstones. We encountered one after another of these “tempestades” on the divide between Lambrama and Antabamba in 1911. They are among the most impetuous little storms I have ever experienced. The longest of them raged on the divide from two-o’clock until dark, though in the valleys the sun was shining. Fortunately, in this latitude they do not turn into heavy snowstorms as in the Cordillera of northwestern Argentina, where the passes are now and then blocked for weeks at a time and loss of human life is no infrequent occurrence.[35] They do, however, drive the shepherds down from the highest slopes to the mid-valley pastures and make travel uncomfortable if not unsafe.

ABSTRACT FROM DAILY WEATHER OBSERVATIONS, SANTA LUCIA, 1913-14

NOVEMBER

“Tempest” recorded 11 times, distant thunder and lightning 9 times. Unusual weather records: “clear sky, scorching sun, good weather” (Nov. 29); “morning sky without a single cloud, weather agreeable” (Nov. 30).

DECEMBER

Clear morning sky 6 times. Starry night or part of night 7 times. Beginning of rain and strong wind frequently observed at 5-6 P.M. “Tempest” mentioned 19 times--5 times at midnight, 8 times at 5-6 P.M.

JANUARY

Clear morning sky 5 times. Starry night 3 times. Rain, actual or threatening, characteristic of afternoons. “Tempest,” generally about 5-6 P.M., 7 times. Sun described 4 times as scorching and, when without wind, heat as stifling. Weather once “agreeable.”

FEBRUARY

Constant cloud changes, frequent afternoon or evening rains. “Tempest,” generally 4 P.M. and later, 16 times.

MARCH

Twice clear morning skies, once starry night. Scorching sun and stifling heat on one occasion. “Tempest,” generally in late afternoon and accompanied by hail, 19 times. Observed 3 or 4 times a strong, “land breeze” (terral) of short duration (15-20 mins.) and at midnight.

MOROCOCHA

Morococha, in the Department of Ancachs, Peru, lies in 76° 11′ west longitude and 11° 45′ south latitude and immediately east of the crest line of the Maritime Cordillera. It is 14,300 feet above sea level, and is surrounded by mountains that extend from 1,000 to 3,000 feet higher. The weather records are of special interest in comparison with those of Santa Lucia. Topographically the situations of the two stations are closely similar hence we may look for climatic differences dependent on the latitudinal difference. This is shown in the heavier rainfall of Morococha, 4° nearer the equatorial climatic zone. (For location see Fig. 66.)

The meteorological data for 1908-09 were obtained from records kept by the Morococha Mining Company for use in a projected hydro-electric installation. Other data covering the years 1906-11 have appeared in the bulletins of the _Sociedad Geográfica de Lima_. These are not complete but they have supplied rainfall data for the years 1910-11;[36] those for 1906 and 1907 have been obtained from the _Boletín de Minas_.[37]

TEMPERATURE

The most striking facts expressed by the various temperature curves are the shortness of the true winter season--its restriction to June and July--and its abrupt beginning and end. This is well known to anyone who has lived from April to October or November at high elevations in the Central Andes. Winter comes on suddenly and with surprising regularity from year to year during the last few days of May and early June. In the last week of July or the first week of August the temperatures make an equally sudden rise. During 1908 and 1909 the mean temperature reached the freezing point but once each year--July 24 and July 12 respectively. The absolute minimum for the two years was -22° C. July of 1908 and June of 1909 are also the months of smallest diurnal variability, showing that the winter temperatures are maintained with great regularity. Like all tropical high-level stations, Morococha exhibits winter maxima that are very high as compared with the winter maxima of the temperate zone. In both June and July of 1908 and 1909 the maximum was maintained for about a week above 55° F. (12.8° C.), and in 1909 above 60° F. (15.6° C.), the mean maximum for the year being only 4.7° F. higher. For equal periods, however, the maxima fell to levels about 10° F. below those for the period from December to May, 1908.

It is noteworthy that the lowest maximum for 1909 was in October, 44° F. (6.7° C.); and that other low maxima but little above those of June and July occur in almost all the other months of the year. While 1909 was in this respect an exceptional year, it nevertheless illustrates a fact that may occur in any month of any year. Its occurrence is generally associated with cloudiness. One of the best examples of this is found in the January maximum curve for 1909, where in a few days the maxima fell 12° F. Cloud records are absent, hence a direct comparison cannot be made, but a comparison of the maximum temperature curve with the graphic representation of mean monthly rainfall, will emphasize this relation of temperature and cloudiness. February was the wettest month of both 1908 and 1909. In sympathy with this is the large and sharp drop from the January level of the maxima--the highest for the year--to the February level. The mean temperatures are affected to a less degree because the cloudiness retards night radiation of heat, thus elevating the maxima. Thus in 1908 the lowest minimum for both January and February was 28.4° F. (-2° C.). For 1909 the minima for January and February were 27.5° F. (-2.5° C.) and 29.3° F. (-1.5° C.) respectively.

The extent to which high minima may hold up the mean temperature is shown by the fact that the mean monthly temperature for January, 1908, was lower than for February. Single instances illustrate this relation equally well. For example, on March 5th, 1908, there occurred the heaviest rainfall of that year. The maximum and minimum curves almost touch. The middle of April and late September, 1909, are other illustrations. The relationship is so striking that I have put the two curves side by side and have had them drawn to the same scale.

FREQUENCY OF THE DIURNAL VARIABILITY, MOROCOCHA, 1908 AND 1909

1908 ----------------------------------------------------------------- Degrees | | | | | | | | | | | | |Total No. F. | J.| F.| M.| A.| M.| J.| J.| A.| S.| O.| N.| D.| of days --------+---+---+---+---+---+---+---+---+---+---+---+---+--------- 0 | --| 3 | 2 | 3 | --| --| 2 | 1 | 3 | 1 | 1 | 3 | 19 0-1 | 6 | 5 | 6 |10 | 9 |10 |13 |10 | 8 | 6 | 6 | 5 | 94 1-2 | 4 | 1 | 3 | 7 | 5 | 3 | 7 | 7 | 8 | 6 | 6 | 4 | 61 2-3 | 6 | 1 | 3 | 4 | 9 | 2 | 2 | 4 | 4 | 7 | 7 | 4 | 53 3-4 | 5 | 3 | 2 | 3 | 3 | 4 | 2 | 9 | 4 | 5 | 3 | 5 | 48 4-5 | 2 | 3 | 1 | 1 | 2 | 5 | 5 | --| 1 | 1 | 6 | 3 | 30 Over 5 | 3 | 4 | 3 | 2 | 3 | 6 | --| --| 2 | 5 | 1 | 5 | 34 --------+---+---+---+---+---+---+---+---+---+---+---+---+--------- Days per|26 |20 |20 |30 |31 |30 |31 |31 |30 |31 |30 |20 | 339 month | | | | | | | | | | | | | ------------------------------------------------------------------ 1909 --------------------------------------------------------------------- | | | | | | | | | | | | | |Mean Degrees | | | | | | | | | | | | |Total |for F. | J.| F.| M.| A.| M.| J.| J.| A.| S.| O.| N.| D.|No. of|1908 | | | | | | | | | | | | | days |-1909 --------+---+---+---+---+---+---+---+---+---+---+---+---+------+----- 0 | 6 | 1 | 4 | 2 | 1 | 2 | 4 | 4 | 3 | 6 | 2 | 1 | 36 | 27.5 0-1 | 9 | 8 | 5 | 6 | 6 | 7 | 8 |13 | 9 | 4 |11 |10 | 96 | 95 1-2 | 4 | 6 | 8 | 3 |11 |14 | 3 | 3 | 5 | 3 | 9 | 6 | 75 | 68 2-3 | 3 | 7 | 4 | 8 | 4 | 3 | 6 | 6 | 4 | 6 | 1 | 3 | 55 | 54 3-4 | 4 | 5 | 3 | 6 | 4 | 4 | 4 | 3 | 6 | 3 | 2 | 5 | 49 | 48.5 4-5 | 1 | 1 | 5 | 1 | 2 | --| 2 | 1 | 1 | 2 | --| 2 | 18 | 24 Over 5 | 4 | --| 2 | 4 | 3 | --| 4 | 1 | 2 | 7 | 5 | 3 | 35 | 34.5 --------+---+---+---+---+---+---+---+---+---+---+---+---+------+----- Days per|31 |28 |31 |30 |31 |30 |31 |31 |30 |31 |30 |30 | 364 |351.5 month | | | | | | | | | | | | | | ---------------------------------------------------------------------

RAINFALL

The annual rainfall of Morococha is as follows:

1906 28 inches ( 712 mm.) 1907 40 " (1,011 mm.)[38] 1908 57 " (1,450 mm.) 1909 45 " (1,156 mm.) 1910 47 " (1,195 mm.) 1911 25 " ( 622 mm.)

The mean for the above six years amounts to 40 inches (1,024 mm.). This is a value considerably higher than that for Caylloma or Santa Lucia. The greater rainfall of Morococha is probably due in part to its more northerly situation. An abnormal feature of the rainfall of 1908, the rainiest year, is the large amount that fell in June. Ordinarily June and July, the coldest months, are nearly or quite rainless. The normal concurrence of highest temperatures and greatest precipitation is of course highly favorable to the plant life of these great altitudes. Full advantage can be taken of the low summer temperatures if the growing temperatures are concentrated and are accompanied by abundant rains. Since low temperatures mean physiologic dryness, whether or not rains are abundant, the dryness of the winter months has little effect in restricting the range of Alpine species.

The seasonal distribution of rain helps the plateau people as well as the plateau plants. The transportation methods are primitive and the trails mere tracks that follow the natural lines of topography and drainage. Coca is widely distributed, likewise corn and barley which grow at higher elevations, and wool must be carried down to the markets from high-level pastures. In the season of rains the trails are excessively wet and slippery, the streams are often in flood and the rains frequent and prolonged. On the other hand the insignificant showers of the dry or non-growing season permit the various products to be exchanged over dry trails.

The activities of the plateau people have had a seasonal expression from early times. Inca chronology counted the beginning of the year from the middle of May, that is when the dry season was well started and it was inaugurated with the festivals of the Sun. With the exception of June when the people were entirely busied in the irrigation of their fields, each month had its appropriate feasts until January, during which month and February and March no feasts were held. April, the harvest month, marked the recommencement of ceremonial observances and a revival of social life.[39]

In Spanish times the ritualistic festivals, incorporated with fairs, followed the seasonal movement. Today progress in transportation has caused the decadence of many of the fairs but others still survive. Thus two of the most famous fairs of the last century, those of Vilque (province of Puno) and Yunguyo (province of Chucuito), were held at the end of May and the middle of August respectively. Copacavana, the famous shrine on the shores of Titicaca, still has a well-attended August fair and Huari, in the heart of the Bolivian plateau, has an Easter fair celebrated throughout the Andes.

COCHABAMBA

Cochabamba, Bolivia, lies 8,000 feet above sea level in a broad basin in the Eastern Andes. The Cerro de Tunari, on the northwest, has a snow and ice cover for part of the year. The tropical forests lie only a single long day’s journey to the northeast. Yet the basin is dry on account of an eastern front range that keeps out the rain-bearing trade winds. The Rio Grande has here cut a deep valley by a roundabout course from the mountains to the plains so that access to the region is over bordering elevations. The basin is chiefly of structural origin.

The weather records from Cochabamba are very important. I could obtain none but temperature data and they are complete for 1906 only. Data for 1882-85 were secured by von Boeck[40] and they have been quoted by Sievers and Hann. The mean annual temperature for 1906 was 61.9° F. (16.6° C.), a figure in close agreement with von Boeck’s mean of 60.8° F. (16° C.). The monthly means indicate a level of temperature favorable to agriculture. The basin is in fact the most fertile and highly cultivated area of its kind in Bolivia. Bananas, as well as many other tropical and subtropical plants, grow in the central plaza. The nights of midwinter are uncomfortably cool; and the days of midsummer are uncomfortably hot but otherwise the temperatures are delightful. The absolute extremes for 1906 were 81.5° F. (27.5° C.) on December 11, and 39.9° F. (4.4° C.) on July 15 and 16. The (uncorrected) readings of von Boeck give a greater range. High minima rather than high maxima characterize the summer. The curve for 1906 shows the maxima for June and July cut off strikingly by an abrupt drop of the temperature and indicates a rather close restriction of the depth of the season to these two months, which are also those of greatest diurnal range.

The rainfall of about 18 inches is concentrated in the summer season, 85 per cent falling between November and March. During this time the town is somewhat isolated by swollen streams and washed out trails: hence here, as on the plateau, there is a distinct seasonal distribution of the work of planting, harvesting, moving goods, and even mining, and of the general commerce of the towns. There is an approach to our winter season in this respect and in respect of a respite from the almost continuously high temperatures of summer. The daytime temperatures of summer are however mitigated by the drainage of cool air from the surrounding highlands. This, indeed, prolongs the period required for the maturing of plants, but there are no harmful results because freezing temperatures are not reached, even in winter.

MONTHLY TEMPERATURES, COCHABAMBA, 1906

-------------+-------------+-------------+-------------+-------------- Month | Mean Min. | Mean Max. | Mean Range | Daily Mean -------------+-------------+-------------+-------------+-------------- January | 55.7 | 72.25 | 16.65 | 63.3 February | 61.2 | 71.3 | 10.1 | 65.5 March | 59.8 | 72.6 | 12.8 | 65.5 April | 55.06 | 70.8 | 15.74 | 62.2 May | 50.9 | 68.7 | 17.8 | 59.1 June | 47.1 | 65.6 | 18.5 | 55.6 July | 44.8 | 64.9 | 20.1 | 54.1 August | 49.9 | 68.0 | 18.1 | 58.2 September | 55.6 | 73.2 | 17.6 | 63.7 October | 56.1 | 73.4 | 17.3 | 64.0 November | 58.1 | 75.7 | 17.6 | 66.2 December | 58.6 | 73.9 | 15.3 | 65.8 -------------+-------------+-------------+-------------+--------------

FREQUENCY OF DIURNAL VARIABILITY AT COCHABAMBA, 1906

-------+----+----+----+----+----+----+----+----+----+----+----+----++------ | | | | | | | | | | | | ||Total Degrees| | | | | | | | | | | | ||No. of F. | J. | F. | M. | A. | M. | J. | J. | A. | S. | O. | N. | D. || days -------+----+----+----+----+----+----+----+----+----+----+----+----++------ 0 | 1 | 3 | 10 | 12 | 6 | 10 | 9 | 6 | 9 | 6 | 3 | 4 || 79 0-1 | 5 | -- | 3 | 5 | 3 | 3 | -- | 4 | -- | 3 | 1 | 1 || 28 1-2 | 10 | 10 | 13 | 11 | 15 | 7 | 14 | 11 | 15 | 10 | 14 | 13 || 143 2-3 | 7 | 11 | 3 | 1 | 5 | 8 | 7 | 4 | 3 | 6 | 7 | 6 || 68 3-4 | 6 | 2 | 2 | 1 | 2 | 2 | 1 | 6 | 3 | 4 | 3 | 5 || 37 4-5 | -- | -- | -- | -- | -- | -- | -- | -- | -- | 1 | 1 | 1 || 3 Over 5 | 2 | 2 | -- | -- | -- | -- | -- | -- | -- | 1 | 1 | 1 || 7 -------+----+----+----+----+----+----+----+----+----+----+----+----++------

A series of curves shows the daily march of temperature at various locations along the seventy-third meridian. Figs. 109 to 113 are for the Urubamba Valley. Respectively they relate to Pongo de Mainique, 1,200 feet elevation (365 m.), the gateway to the eastern plains; Yavero, 1,600 feet (488 m.), where the tributary of this name enters the main stream; Santo Anato, 1,900 feet (580 m.); Sahuayaco, 2,400 feet (731 m.), and Santa Ana, 3,400 feet (1,036 m.), one of the outposts of civilization beyond the Eastern Cordillera. The meteorological conditions shown are all on the same order. They are typical of dry season weather on the dry floor of a montaña valley. The smooth curves of clear days are marked by high mid-day temperatures and great diurnal range. Santo Anato is a particularly good illustration: the range for the 24 hours is 38° F. (21.1° C.). This site, too, is remarkable as one of the most unhealthful of the entire valley. The walls of the valley here make a sharp turn and free ventilation of the valley is obstructed. During the wet season tertian fever prevails to a degree little known east of the Cordillera, though notorious enough in the deep valleys of the plateau. The curves show relative humidity falling to a very low minimum on clear days. At Santo Anato and Santa Ana, for example, it drops below 30 per cent during the heat of the day. Afternoon cloudiness, however, is a common feature even of the dry season. A typical afternoon cloud formation is shown in Fig. 114. The effect on temperature is most marked. It is well shown in the curve for August 20 and 22 at Yavero. Cloudiness and precipitation increase during the summer months. At Santa Ana the rainfall for the year 1894-95 amounted to 50 inches, of which 60 per cent fell between December and March. For a discussion of topographic features that have some highly interesting climatic effects in the eastern valleys of Peru see Chapter VI.

Abancay, 8,000 feet (2,440 m.), in one of the inter-Andean basins, is situated in the zone of marked seasonal precipitation. The single day’s record shows the characteristic effect of cloud reducing the maximum temperature of the day and maintaining the relative humidity.

Camp 13, 15,400 feet (4,720 m.), lies near the crest of the Maritime Cordillera a little south of Antabamba. Afternoon storms are one of its most significant features. Cotahuasi, 9,100 feet (2,775 m.) is near the head of a west-coast valley. Its low humidity is worthy of note. That for Salamanca, 12,700 feet (3,870 m.), is similar but not so marked.

Aplao, 3,100 feet (945 m.), and Camaná at the seacoast are stations in the west-coast desert. The interior location of the former gives it a greater range of temperature than Camaná, yet even here the range is small in comparison with the diurnal extremes of the montaña, and the tempering effect of the sea-breeze is clearly apparent. Camaná shows a diurnal temperature range of under 10° F. and also the high relative humidity, over 70 per cent, characteristic of the coast.