Pakistan is situated between 23°N to 37°N and 60°E to 76°E, on the western confines of the SW Monsoon (SWM) over subcontinent. Its climate is mainly arid to semiarid having a small area with sub humid climate. Pakistan being an agricultural state depends on water resources like rainfall, glacial ice melt etc. Precipitation is received in both summer and winter seasons. Western disturbances approach the upper parts of the country throughout the year while Easterlies are dominant in summer. In summer heavy falls are mainly due to superposition of easterly and westerly.
The dominant air mass that impacts Pakistan is mostly Tropical (due to low latitude and warm weather) and mostly Continental (although one part of it is in contact with the ocean, the land is mostly inland). Towards the coast, the climate varies from warm to breezy, however as the country progresses more inland, there are higher elevations and generally cooler temperatures. The changing of the seasons is characterized by a cold, dry winter, a hot and dry winter, and a wet summer of monsoons. Pakistan is affected by the trade winds. Pakistan is also in close proximity to the Indian Ocean. The most abundant source of rainfall in Pakistan is in the form of the southwest monsoon, a natural occurrence that causes intense floods. It is common because of Pakistan’s proximity to the cold regions of Asia (Himalayas). Monsoons blow from the cold to warm regions so the wind that blow through regions such as the Himalayas bring the monsoons to Pakistan.
Pakistan is located between the upper-level easterly subtropical jet to the south and the westerly mid-latitude jet to the north. At mid-levels, typically dry and diurnally heated air flows off the Afghan Plateau. This dry subsiding flow occasionally provides a stable cap over low-level moisture advected into the foothills of northern Pakistan from the Arabian Sea, and intense deep convection in the northwest indentation of the Himalayas occurs when convection breaks through the cap. Mean conditions at both 700 and 850 hPa indicate low-to mid-level westerly wind components throughout south to central India. During the monsoon season, atmospheric moisture is maximized over the Bay of Bengal and Arabian Sea as evaporative latent heat fluxes act to increase the moisture content in the boundary layer. This moist air flows onto the continent in a generally southwesterly direction in response to the thermally driven monsoon circulation. As the moist air encounters topographic features of various scales, in the Hindu Kush and Sulaiman ranges of Afghanistan, the Himalayas, and the Arakan range of Burma, precipitation tends to be maximized upstream of and over the windward slopes of such features. However, the typical monsoon precipitation in Pakistan is notably small with the exception of the northern part of the country that experiences frequent deep convection near the intersection of the Hindu Kush and Himalayan ranges. Pakistan is generally dry and arid, even during the monsoon season; thus, anomalously large amounts of precipitation in the region are unexpected and can have catastrophic impacts (for normal climate of Pakistan, see Figure 1.1).
Climate induced natural disasters in Pakistan
A mini tornado (twister) had hit Peshawar valley with a speed of 110 km/hr and reported rainfall of 60 mm on 27th April, 2015, causing huge damages. It was very unusual extreme weather event that rarely occur in Pakistan. In the past, same type of windstorms (tornados) occurred as;
1. In March 2001, in Village “Chak Misran”, Tehsil Bhalwal, District Sargodha with a speed of 193 km/hr, 20 reported dead & 40 injured.
2. In March 2011, in Village “Bahadur Pur”,near Head Marala, District Sialkot with a speed of 100 km/hr, 10 reported dead & 32 injured.
According to the climate of Pakistan, such types of extreme weather events rarely develop due to thermal contrast during the months of March or April (a transition period, when days are getting hot and nights are still cold) due to interaction of cold air mass (from westward) & warm air mas (from east or south). For Peshawar, “Rain with Dust-Thunderstorm” was predicted two days before by PMD with today’s advancement in radar and satellite technologies. The occurrence of such high impact weather events (extremes) revealed that the consequences of Climate Change, due to deforestation, urbanization & pollution have already happening in Pakistan and the probability of such extreme events would be high in the future.
People of Pakistan witnessed a heatwave event in southern parts of the country including from 17th to 24th June 2015. This heatwave event took more than 1200 human lives in Karachi and about 200 lives in other parts of Sindh province. Main cause of deaths was heatstroke and dehyderation during extreme temperatures. In Karachi maximum temperature of 44.8°C was recorded which is second highest temperature after the year 1979. The intensity of heat index or apparent temperature was calculated to be 66°C on the peak heatwave day i.e. 20th June 2015. The heat wave was a symptom of global climate change, aggravated by deforestation, expansion of asphalt superhighways, and rapid urbanisation.
On the night falling between 15th and 16th July, and again on 19th , 24th and 28th July 2015, different parts of District Chitral were hit by Glacial Lake Outburst Floods (GLOF) which carried massive torrents and flash floods washing away villages, access roads, bridges, drinking water supply systems, micro hydel power channels, public/private property and agricultural crops. This phenomenon is unusual; however, due to climate changes, districts in the north of Khyber Pakhtunkhwa i.e. Mansehra, Chitral, Battagram, Kohistan (U/L), Torghar and Shangla are prone to such incidents of GLOF. Met Office predicted that monsoon currents would penetrate in upper parts of the country in coming days. A westerly wave was also likely to approach northern areas of the country during that weekend. Scattered rain/thundershowers were expected in Punjab, Khyber Pakhtunkhwa, FATA, Gilgit Baltistan and Kashmir during Saturday to Monday with isolated heavy falls in Malakand, Hazara, Mardan, Peshawar, Rawalpindi, Gujranwala and Lahore divisions, Upper FATA and Kashmir. The clear sky conditions and high temperatures of northern areas during next two days had a potential to produce more glacier-melt during the weekend. Rainfall over the glaciers triggered the melt rate, causing more flash floods in the local rivers and streams of the northern areas (Gilgit-Baltistan and Malakand Division including Chitral) during that weekend. There was an increased risk of GLOF in Gilgit-Baltistan and District Chitral during the period. Local communities were advised to remain alert and concerned authorities to take precautionary measures.
The earliest snowfall in 40 years had dumped up to four feet of snow on one town in less than 24 hours. Snowstorm in Babusar area of Pakistan had claimed life of a person. Snowfall came early this year. It started lashing Kaghan Valley on 24th Oct 2015 and continued intermittently for a second consecutive day on 25th Oct 2015. The area from Naran to Babusar Top received up to four feet of snow, leaving the roads blocked and over 1,200 tourists, including women and children, from across the country stranded. They faced difficulties as they ran out of supplies amidst continuous rain and snowfall. The snowfall has also damaged the power lines and some small bridges. Met office predicted snowfall over the hills of Malakand division, GB and Kashmir during the period.
The anthropogenic climate change and its impacts are worrying the human race. The last century has seen significant increase in global surface temperatures and, in addition, this process of increasing global temperatures will continue (Houghton, et al., 2001), as mentioned in IPCC report, until the emission of CFCs are not controlled. It is important to realize that the need and limited human resources and technology drive towards generation of projections by sampling GCMs and RCP scenarios that are practicable to cultivate, examine and publicise. In addition, these projections should be policy relevant for the region (McSweeney, et al., 2015).
Coupled Model Intercomparision Project Phase 5 (CMIP5), as compared to CMIP3, aggregates superior global climate models (Sillmann, et al., 2013). In addition, the availability of the simulations, generated from modern climate models (GCMs), encourage climate researchers do their climate research within the realm of CMIP5. This research can include not only mean climate but the weather-extremes as well. Since the extremes are slightly less predictable, therefore, to mark their period and strength, it is necessary to explore long duration data sets of actual data (Houghton, et al., 2001). In the CMIP5 experiment it was agreed to grant access to the instantaneous fields of prognostic variables from GCMs to be used as lateral boundary conditions (LBCs) to steer regional climate models (RCMs). It opened the gates for researchers to downscale with diverse combinations of GCMs and RCMs or statistical downscaling methods to explore variety of high-resolution projections for different regional areas of the world (McSweeney, et al., 2015).
It is accepted by all that mortals are effected severely with the changes in frequency and intensity of extreme events (Sohrabi, et al., 2013). Indices based on Percentile, threshold, duration and on other statistical measures can be used to describe extreme events (Houghton, et al., 2001). To examine the extremes, the Expert Team on Climate Change Detection and Indices (ETCCDI) has introduced a set of climate indices which are used globally for analyzing changing extremes in observed data (Sillmann, et al., 2013). These indices are also used for future climate projections. The ETCCDI indices help in conceiving a detailed picture of temperature and precipitation over a region (Sillmann, et al., 2013). The study of extreme events require data from greater number of long term weather records of the region. But, lack of funding, human resource, technology and political instability are the main obstacles in developing countries in maintaining healthy and quality controlled weather data repositories (Choi, et al., 2009). According to Sillmann, et al., (2008) a number of researchers focused on data gathered from ground weather stations and meteorological observatories as Frich, et al., (2002) and Klein Tank, et al., (2003) did for studying climate extreme indices while several also used future climate projections like (Meehl, et al., 2000) (Meehl, et al., 2004) (Tebaldi, et al., 2006).
The key to build mitigation and adaptation plans against extreme events due to climate change, microscopic examination of extreme events in terms of intensity, duration and frequency is necessary (Choi, et al., 2009). An effort is made to comprehensively evaluate extreme indices on the scale of modern CMIP5 models for Pakistan, at province level. This type of comparison between indices calculated from observational data and multi-model simulations has not been done before, specially keeping the policy makers for provinces in mind. It is seen that multimodel ensemble simulations are quite better than individual models in providing healthier estimates of future climate variations and model related reservations (Sillmann, et al., 2013).
The onward analysis explores the selection of different GCMs from CMIP5 ensemble for Pakistan at province level. In this way we found 5 different subsets of CMIP5 GCMs for 5 different province groups. Moreover, the same technique is also adopted for CORDEX (McSweeney, et al., 2015) and Nex-NASA. Afterwards, extreme indices for observed, simulated and projected climate are found and analyzed on provincial basis over the country.