Spatial distribution of secular trends in annual and seasonal precipitation over Pakistan

Abstract

The presence of autocorrelation and long-term persistence (LTP) can lead to considerable change in the significance of trends in hydro-climatic time series. This therefore casts doubt on past findings of climatic trend studies that did not consider LTP. We assessed the trends in spatio temporal patterns of annual and seasonal precipitation of Pakistan in recent years (1961-2010) using precipitation data from the Global Precipitation Climatology Centre (GPCC) using (1) the ordinary Mann-Kendall (MK) test and (2) the modified Mann-Kendall (MMK) test, which can discriminate LTP from unidirectional trends. The results indicate that significance in trends obtained using the MK test is reduced when LTP is taken into consideration. The annual precipitation in Pakistan is increasing in the northern highlands and a few places in the sub- Himalayan ranges in northeast Pakistan, where monsoon precipitation is also increasing. There is no indication of significant change in winter precipitation. Post-monsoon precipitation is in - creasing at a few locations in the monsoon-dominated southeast region and decreasing in the southwestern arid region.