Trends in heat wave related indices in Pakistan

Increased frequency and severity of heat wave is one of the immediate and certain impacts of rising temperature due to global warming. A number of heat wave related indices considering both daily maximum and minimum temperature are proposed in this paper to assess the changes in different characteristics of heat waves in Pakistan, which is one of the most vulnerable countries of the world to extreme temperature. Gridded daily temperature dataset of Princeton's Global Meteorological Forcing for the period 1948-2010 was used for this purpose. The results revealed daily maximum temperature more than 95-th percentile threshold for consecutive 5days or more can well reconstruct the spatial pattern of heat wave in Pakistan. The results revealed that intense heat waves in Pakistan are mostly occurred in the southwest. However, heat waves are most devastating when those occur in highly populated southeast region. It was found that major heat waves in Pakistan occurred in 1952, 1978, 1984, 1988, 2002, 2006, 2009 and 2010 which affected 55.7, 71.1, 74.0, 72.3, 48.9, 60.6, 41.8 and 82.9% population respectively. The trends in heat wave indices revealed significant increases in the indices calculated based on both the maximum and minimum temperatures. Duration of heat wave was found to increase at a rate of 0.71days/decade, while the duration and affected area having both maximum and minimum temperature above 95-th percentiles are found to increase at a rate of 0.95days/decade and 1.36% of total area of Pakistan per decade respectively.