In this research, De Martonne’s index of aridity (IDM), Pinna combinative aridity index (IP), and UNEP aridity index (AI) were used for the drought analysis in the Sirvan river basin, Iran, during the period 2002–2018. Spatiotemporal analysis of aridity indices on each station was determined by calculating the Z statistic value of the nonparametric Mann–Kendall (MK) method of time series on the index values, and the slope of trend lines was calculated by Sen’s slope estimator method. The percentage change (tv%) in the amount of indicators was obtained during the studied period for each station. The results showed that eight stations out of 10 studied stations had a downward trend and the other stations had an upward trend (close to zero and nonsignificant) for the IDM on an annual scale, and one station (Janevareh, Z = −1.66) was statistically significant at the level of 10%. In the IP method, five stations had a downward trend, and the station (Janevareh, Z = −1.93) was statistically significant at the level of 10%. Also, in the AI method, nine stations had a downward trend, and the station of Janevareh (Z = 1.93) was statistically significant at the level of 10%. Among the stations that have experienced the highest amount of drying, Sarcheshmeh station in IDMwith a slope of −0.45, Janevareh station in IP with a slope of −0.22, and Sarcheshmeh and Janevareh stations in AI index with a slope of −0.01 and more have tended toward drying, respectively. In general, it can be concluded that the climate of most of the studied stations in the Sirvan river basin has become significantly drier and warmer.
