Abstract

This study aims to estimate the potential changes in rainfall erosivity under future climatic conditions in the Upper Nan watershed, Thailand. The multi-climate model and multi-emission scenario approach for the estimation of climate change impacts used in the study consists of PRECIS: ECHAM4, GFDLR-30, HadCM3 and NCAR CCSM3. The change factor or the delta change method is used as a downscaling technique to generate future precipitation. The relationship between monthly precipitation and rainfall erosivity can be used to estimate monthly rainfall erosivity under future climate. Results indicate that the average annual precipitation for all three future time slices increases from a baseline value of 1250 mm by between 2.14% (1277 mm) in 2011-2040 and 7.00% (1337 mm) in 2071-2099. Moreover, the mean of each GCM and emission scenario combination illustrates an increase in average annual rainfall erosivity for all three future time slices; from a baseline value of 5503 MJ mm ha-1 h-1 yr-1, the amount increases by between 5.02% (5779 MJ mm ha-1 h-1 yr-1) in 2011−2040 to 14.20% (6284 MJ mm ha-1 h-1 yr-1) in 2071-2099. According to RUSLE, a 1% increase in rainfall erosivity will lead to a 1% increase in soil erosion, if other factors remain constant. Therefore, soil erosion in the Upper Nan watershed is projected to be more serious in the coming decades.

Keywords: Rainfall erosivity; Precipitation; Climate change; Upper nan watershed