This paper propounds an improved kinetic model of monthly potential evapotranspiration E_Ti:

where i is a number of month, P_i the monthly mean atmospheric pressure(mb),t_i the monthly mean air temperature(℃),d_i the number of days in a month,U_i the monthly mean wind velocity measured at height 10-12m (m/s),w_oi the saturated water vapour pressure at t_i(mmHg),and h_i the monthly mean relative humidity. The monthly aridity k_i=E_Ti/r_i, where r_i is the monthly precipitation (mm);and the annual aridity K=(ΣE_Ti)/r_α,where r_α is the annual precipitation (mm).The soil moisture regime is udic when K<1, ustic when 1≤K<3.5, and aridic when K≥3.5. If k_i<0.7 for 8-12 months including May-September and t_i>1.5 for other months, then the soil moisture regime is perudic.