Downscaling model in agriculture in Western Uzbekistan climatic trends and growth potential along field crops physiological tolerance to low and high temperatures.

The Global climate change is becoming an increasing challenge for agriculture. Beyond the increased local occurrence of extreme events high temperatures are becoming an increasingly present limiting factor in crop production. The agriculture in the West of Uzbekistan with very limited rainfalls is highly dependent on irrigation schemes using the Amu Darya water flow. With low Winter (freezing nights with minimum air temperatures of less than 0 °C) and high Summer temperatures (hot days and nights with temperatures above 35 °C during daylight, and minimum air temperatures of more than 20 °C during night time - tropical nights) the local continental arid climate temperatures are a main limiting factor faced by the local agriculture. The arid climate, with a crop production dependant on irrigation, allows putting the focus on temperatures influence on field crops, while rainfalls have barely any influence. In temperate countries the focus has mainly been on low temperatures as a main limiting factor. Freeze is indeed influencing the sowing period and putting crops at early development stages at risk. Even though, the West of Uzbekistan is facing low temperatures over the Winter period which is also challenging the local agriculture, high temperatures are becoming an increasing threat over the Summer period. The present study is analysing day and night temperature trends over the period 1987-1990 and 2013-2017. The observed trends are further compared with data from the Intergovernmental Panel on Climate Change (IPCC) model available on the World Bank open portal. Regression lines have been calculated illustrating the trends over the period. The inter-annual temperature variations are important with a relative standard deviation which ranges between 16 and 50%. The trend is considered as not significant when the relative standard deviation exceeds the variation over the overall time-period. The Day degrees are used to provide an insight into the climatic impact on crop growth along plants physiological tolerance. The day degree methodology has been especially adjusted in the present publication in order to take into account the tolerance of the studied crops to high temperatures. While the hot period is progressively expending into the Spring period, Winters are not becoming much milder limiting the benefit for Winter crops. While the hot days and tropical night event will become predominant over the Summer period the yields in cotton and rice are expected to drop drastically over the second half of the XXIst century. The expected reduction of water inflow of the Amu Darya over the century will further strongly put into question the crop production model in the West of Uzbekistan. The present publication aims at describing the ongoing trends, expectable changes in agricultural production and timelines. It is also illustrating how hot temperatures analysis could be integrated in downscaling models in agriculture in other regions of Uzbekistan and of the world.