Temporal analysis of wheat yield and climatic trends in Pakistan

Introduction Climate is the major driving force of crop production, water use and agriculture is one of the most vulnerable sectors to climate change. Around 40% to 50% of the Earth’s surface area consists of agricultural lands, comprises the land which is used for the cultivation of crops, land used as grasslands and also of stable harvest or crops which encompasses the agro-forestry and crops used for bio-energy (Cai et al., 2007). Climate change, according to the definition by the Intergovernmental Panel on Climate Change (IPCC) (2001), refers to any change in climate over time whether due to natural variability or as a result of human activity. Many of the climate change factors affecting agriculture yield and agricultural productivity includes rainfall distribution, temperature, variation in sowing and harvesting time, water availability, evapotranspiration and land suitability. Climate change impact on agriculture is several folds, together with diminishing of agricultural output and reduction in growth period for crops (Edwards, 1999). Wheat is such an important crop that out of total world’s food requirement 21% is fulfilled through wheat and globally the area used for wheat production is 200 million. Wheat is also traded at international level and 43% of import is contributed by the developing countries, but 81% of the wheat consumed in developing countries is the production of their own (CIMMYT, 2005). In Pakistan, outstanding progress has been attained in the sector of wheat since Green Revolution. Wheat is the most important agricultural commodity of Pakistan and it accounts for 13.8% in value added in agriculture and 3.4% in GDP (GoP, 2004). Wheat is taken as targeted commodity in Pakistan mainly because it is a vital product in the diet of those who are below the poverty line, and in addition it characterizes a significant commodity in terms of its input to national food security. Many researches have been related to climate change and latest researches have predicted that due to climate change the pattern of rain fall and variation in temperature can occur, and the temperature increase at the end of the century in South Asia is predicted to be 3-4 °C (DEFRA, 2005). Efforts to study the impacts of climate change on production pattern have employed a variety of approaches, including time series analysis (Nicholls, 1997; Thompson, 1975), crop simulation modeling (Andresen, 2001; Bell and Fischer, 1994; Pathak et al., 2003) and spatial analysis of yield trends (Lobell and Asner, 2003). Assessing climate impacts on agriculture have increasingly become major areas of scientific concerns, e.g. valuation of climate impacts on wheat production (Rajin et al., 2007; Wei et al., 2005; Yang et al., 2011). In Pakistan, a study was conducted and Vector Auto Regression (VAR) model was used for this purpose in which trends for climate change impact on production of wheat for the period of 2010-2060 were captured. The results revealed that global climate change might influence the wheat production in Pakistan. Similarly in Swat and Chitral districts of Pakistan, potential future impacts of climate change on wheat yields were assessed (Hussain and Mudasser, 2007). The possible effects due to climate change on the production of wheat were predicted to be various, such as in India it was predicted that due to climate change, reduction in the wheat grains occurred especially in the areas of eastern plains, which had relatively lesser potential (Chandna et al., 2004). By the help of tools of GIS (Geographic Information System), various scientists in different parts of world have predicted the yield of crops and effect of changing environmental factors on the crops and results of their findings have been represented in the form of geographical maps for the better understanding. GIS was used to predict the impact of global warming on the Middle East region, Hashemite Kingdom of Jordan through spatial analysis and meteorological data (Matouq, 2008). Liu et al. (2009) conducted a study to analyze the impact of climatic variables on wheat production. A study was done to quantify the production potential of winter wheat in the North China Plain (NCP) taking into account the spatial and temporal variability caused by climate (Wu et al., 2006). Similarly, crop simulation model (DSSAT) was used to assess