» Altitude also affects annual rainfall or precipitation patterns. Up to about 3,000 meters, annual rainfall totals increase as the altitude increases; thereafter, annual totals diminish with increasing altitude and latitude. In addition to this latitudinal differentiation in rainfall, two other patterns can be discerned. First, given the northwestward movement of the moisture-laden summer monsoon (June to September), the amount of annual rainfall generally decreases from east to west.
The amount of precipitation resulting from the northeast land trade winds varies considerably but increases markedly with elevation. The secondary winter precipitation in the form of snowfalls in the Himalayas is important for generating a sufficient volume of spring and summer meltwaters, which are critical for irrigation in the lower hills and valleys where agriculture predominates.
» In addition, there are seasonal variations in the amount of rainfall, depending on the monsoon cycle. Bishop divides the monsoon cycle into four seasons: premonsoon, summer monsoon, postmonsoon, and winter monsoon. The premonsoon season generally occurs during April and May; it is characterized by the highest temperatures, reaching 40° C during the day in the Tarai Region and other lowlands. The hills and mountains, however, remain cool.
| Nepal has four climatic seasons