Regionalizing precipitation characteristics of Helmand Basin in Afghanistan using TRMM Satellite Product

Although the total amount of precipitation in climate surveys is seen as an important factor in determining climatic conditions, and finally, ecological circumstances, but, its seasonal distribution, and to be more precise, its compliance with environmental requirements, particularly agriculture, is of great importance as well. In this study, we tried to regionalize the annual precipitation totals and the precipitation regime of Helmand basin on a regional scale, which is located in South West Asia, shared between three countries of Afghanistan, Iran and Pakistan. To this end, TRMM satellite rainfall productions with spatial resolution of ۰.۲۵ * ۰.۲۵ degrees for a ۱۵-year period (۲۰۰۰-۲۰۱۴) have been used. To regionalize these two precipitation features in the Helmand basin, the cluster analysis by Ward linkage method was used. Performing the cluster analysis on Helmand basin annual precipitations, it was found that three rainfall areas can be identified in this basin: Eastern high precipitation region with an average annual rainfall of ۲۵۶.۷ mm, Central moderate precipitation region with an average annual rainfall of ۱۷۱.۵ mm and Western low precipitation region with an average annual rainfall of ۸۶.۱ mm. In addition, performing cluster analysis on the relative precipitation per month indicated that two different precipitation regimes, namely, winter precipitation regime and winter- spring precipitation regime can be distinguished in this basin. The winter precipitation regime prevails in the west of the basin, while the winter-spring precipitation regime prevails in the center and east of the basin. The winter precipitation regime is a regime that close to ۶۳.۴% of its total annual precipitation falls in the winter. The winter-spring precipitation regime of this basin is a regime that most of its precipitation occurs first in winter (۴۴%) and then in the spring (۳۰.۵%).