Analysis of recent changes in maximum and minimum temperatures in Pakistan

Abstract

Data from 37 weather stations with records of maximum and minimum temperatures (Tmax and Tmin hereafter) were used to analyse trends in both variables at a monthly, seasonal and annual resolution. Sen's slope and Mann–Kendall statistical tests were applied to calculate the sign and slopes of trends and their statistical significance. A correlation analysis was also performed to study possible relationships between temperatures and certain teleconnection patterns with an influence on Northern Hemisphere temperatures: the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), El Niño-Southern Oscillation (ENSO), and North Sea Caspian Pattern (NCP). The study reveals that Tmax has significantly increased (in over 30% of sites) in the pre-monsoon season and yearly. The sharpest increases were observed in March. Tmin clearly showed positive trends in the pre-monsoon season and at the annual scale. It is also worth noting a cooling trend in the northern areas during the study period. Tmax increased faster than Tmin in the northern areas in all the seasons studied and at annual resolution, while the opposite occurred in the rest of the country (except in the pre-monsoon season).

The highest correlation coefficients between patterns and Tmax and Tmin were seen in the months of the pre-monsoon season: with NAO from January to March; with ENSO in May and with NCP in the late pre-monsoon season (May). AO was the pattern with the lowest relationships with temperatures. These results could have a significant influence on agriculture and water resources in Pakistan if these trends are maintained in the future.