The Republic of Costa Rica

II.

CLIMATE OF COSTA RICA.

The climate of Costa Rica depends on its situation in the tropics, on the position of the sun at different times of the year, and on the topography, but, owing to the narrowness of the country and its situation between the two great oceans, it is well-tempered by the alisios (northeast trades) and other winds.

I begin this chapter with the following table which gives the

Meteorological Conditions in San José During the Year 1896.

First Half of 1897.

The average atmospheric pressure of San José, the capital of the country, is 665.21 mm. The maximum occurs regularly during the months from October to March inclusive, at nine o’clock a. m., and during the rest of the year at eleven o’clock p. m. The minimum occurs always in the afternoon at four o’clock during the first eight months of the year, and at three o’clock during the last four months.

The prevailing wind is from the northeast, or, better, north-northeast and east. During August, September and October an increase of the northwest winds causes the heavy rains of that season. West-northwest and northwest winds blow also from May to August.

The daily variation of winds is generally as follows:

At seven a. m. the most frequent winds blow from S. E., to N. E.; at ten o’clock a. m. from E. to N. N. E; at one o’clock and at four o’clock p. m. from E. N. E. to N.; from seven o’clock p. m. the movement is retrograde. The velocity is least from seven to ten o’clock a. m., and most from one to four o’clock p. m.

In 1889, during the time of observations at San José, there were noted 13 hours of north winds, 186 N. N. E., 571 N. E., 227 E. N. E., 93 E., 58 E. S. E., 25 S. E., 6 S. S. E., S. none, S. S. W. none, 1 S. W., 3 W. S. W., 4 W., 83 W. N. W.

The number of calms is small. The wind is nearly always moderate, but during the dry season the dust whirled up in the cities is very disagreeable. The climate of the uplands is an eternal spring.

The coldest month is January; December and February are relatively cold. The hottest months are May and June. The heat is, at all times, moderate and agreeable. The course of the temperature has all the characters of an insular climate, without having so much humidity. The oscillation of the average temperature is greatest in March and during the dry season, as at that time the sky is clear and the soil exposed to uninterrupted insolation during the day, while the earth’s radiation of heat during the night is rapid. Also the daily oscillation is considerable during the dry season, and continues during the first month of the rainy season, according to the condition of the sky.

In 1890 the sun shone in San José 1911 hours, that is an average of five hours and fourteen minutes per day. February is the month of most sunshine and least nebulosity. The hour of most sunshine during the year is that between eight and nine a. m., and that of the least is in the afternoon.

The oscillation of the temperature of the soil is, at a depth of one meter, 2, 13° C., per year. At a depth of three meters, the temperature of the soil is lowest in February and March, when it is 20, 48° C., and highest in August, when it is 20, 75° C.

The daily variation is almost nothing during the first three months of the year, and the sky is relatively clear, while, from May to October, not one day is clear. During the hottest hours of the day the sky begins regularly to be darkened by clouds, due to ascending atmospheric currents.

In San José the sky is ordinarily clear between midnight and noon, even during the most rainy months, and cloudy the rest of the twenty-four hours. Although the rainfalls are abundant here from May to October, with rare exceptions they do not last more than a few hours each day. The mornings are generally splendid and the air very pure, and nearly every day the sunset can be clearly observed.

From May to November there are about two hours of copious rain daily between one and four o’clock in the afternoon, averaging, with great regularity, from ten to twelve inches a month, and from seventy to eighty inches during the year. Towards the end of June there is a short dry period called “Veranillo de San Juan.”

Through the Desengaño and Palma Passes the northern rains penetrate a short distance every day, and the northern descent of the Palma towards Carillo is probably the most rainy district of the Republic.

At Tres Rios, having an elevation of 4140 feet, six miles east of San José, at the western foot of the Ochomogo Pass, the rain record for 126 days out of ten months showed a fall of 100 inches, while at San José, during the same period of ten months there were 147 rainy days, with a fall of eighty-four inches. In the month of May Professor Pittier, to whom we owe these excellent data, measured nine inches in rainfall in one and one-half hours.

Rainfall in 1896 at Stations of Costa Rica of Different Altitudes,
by Days and Precipitation in Mm.

The daily curve of rainfall shows a minimum very accentuated in the first half of the day. Rain begins to fall about eleven o’clock, and continues to augment rapidly from hour to hour until it reaches its maximum between four and five o’clock p. m.; from this time on it diminishes gradually until morning. The daily maximum of rain is reached about sunset, although in January the heaviest rainfalls are observed between one and two o’clock p. m. The most probable hour of rain is between four and five o’clock p. m. It seldom rains between three and four o’clock, and very seldom during the morning hours.

Thunderstorms reach their maximum in May. The relative humidity of the air is such that the climate can be considered a favored one. Its annual curve shows three minima and three maxima. The minima are observed between February and March, in July, and between November and December; the maxima in June, September and December. These lines, of course, are parallel with those indicating the distribution of rain. The maximum is noted at sunrise, the minimum at two o’clock p. m., with an average oscillation of twenty-four per cent.

From 1866 to 1880, the rain gauge record kept by Mason at San José shows a yearly average precipitation of sixty-four and one-fourth inches, or 1631 millimeters.

It is as follows:

The Rainfall in San José from 1866 to 1880 in Mm.

There is every year a number of slight earthquakes in San José, generally undulating from west to west-northwest, and occurring mostly between eleven p. m. and six a. m. The greatest number are observed at the beginning of the rainy season.

The rainy season on the Caribbean slope of the country does not correspond to that of the Pacific. In fact there are no continuously dry months, and on the northern declivities of the volcanoes of Turialba, Irazú, Barba and Poas, it rains more or less during the entire year; also near Lake Nicaragua it rains nearly continuously, and the mountains of the Guatuso country and the surroundings of the volcano of Orosi are seldom without clouds. At times there are cloud-bursts of tremendous power, broadening rivers for miles. Port Limon is said to have an annual rainfall of eighty-nine inches, but it is greatly exceeded by that of Colon, which averages 120 inches. The mean rainfall at Greytown for 1890, 1891, 1892, was 267 inches yearly. The late United States Commission estimated the average at Lake Nicaragua at eighty inches, and in the basin of the San Juan River at 150 inches.

The climate of Talamanca is for the same reason very unhealthy in the proximity of the coast, and also in the lower course of the rivers a similarly deadly climate prevails. In normal years there are two dry and two wet seasons. The rains commence regularly in May or June and last until the end of July. The months of August and September are more or less dry. In October there are some heavy showers, and extensive rains begin which characterize the months of November, December and January. The driest months are February, March and April. The high region is extremely humid, giving rise to fogs and rains. The mosses which almost completely envelop the stems of the trees are constantly dropping water, and the rivers in this section are almost impassable.

The climate of the great valley of the Rio Grande de Terraba is similar to that described for the terrace lands. Both regions have distinctly marked characters. Rains begin in April, grow heavier towards September, and cease about the end of November. During the rest of the year dry weather prevails, although sometimes heavy showers relieve this arid condition. In the lower zone pronounced radiation causes a heavy dew and extensive fogs, and both are characteristic of this section.

The excessive heat felt on the lowlands diminishes gradually with the rising of the land towards the high mountains, but at times a height of 1500 feet will be found cooler than one of 3000 feet. In the Santa Clara district, for instance, it is cooler at 500 feet elevation than it is in the Reventazon valley at 1500 feet. In general, the torrid lands of the country, ranging from the sea to 150 feet above it, and, if not clear and well-drained, even up to 400 and 500 feet, abound in malarial fevers; but as high ground, having an elevation of from 1500 to 3000 feet is reached, the fevers are of light type and not dangerous, while from 3000 to 5000 feet the diseases are those of the temperate zone, and are due less to local conditions of soil and climate than to personal neglect.

There were no epidemic diseases in 1897. In October 30, 1894, sixteen medical districts were established by law, and so were a number of hospitals and quarantine stations in the ports of the Republic.