Changes And Attribution Of Vegetation In Uzbekistan

Arid zones are very vulnerable to climate change and vegetation is considered central part of vegetation-climate change research studies.Since Uzbekistan's location is arid zone,vegetation-climate relationship analyses play important role in country's agricultural,socialeconomic life.Several scientific research studies have been conducted with respect to vegetation change and its responses to climate variables in regional scale,i.e.over the whole Central Asia.Scientific research studies related to vegetation change and its attributes in Uzbekistan has not so far been conducted as country scale individually in time series.In order to determine vegetation change and its relationship with climate variables,trend analyses have been conducted by Mann-Kendall and Sen's slope estimator for NDVI and climate variables.Three climate variables,i.e.precipitation,solar radiation,temperature have been selected since vegetation is mostly determined by water and energy.Also,seasonal NDVI and climate variables have been checked for trend analyses.In order to determine abrupt point change in NDVI,Mann-Kendall test for abrupt change has been applied and based on this,study time period was split into two sub-periods for further analyses in terms of trend analyses,correlation analyses,and regression analyses.Pearson correlation has been applied to detect relationship of NDVI versus climate variables.In order to check dependence of NDVI on climate variables,single-factor regression and multiple-factor regression have been used.Based on the developed vegetation-climate equation for the first period,contribution of human activities and climate variables on vegetation have been determined and the following results have been obtained:1.Trend analysis of vegetation.NDVI did not significantly change in the period of 1982-2015,but summer NDVI and autumn NDVI significantly decreased during this time period.NDVI insignificantly increased(Z=1.205)during the first time period(1982-2009)and insignificantly(Z=-0.413)decreased during the second time period(2010-2015).2.Trend analysis of climate change.Among climate variables,only temperature significantly increased between 1982-2015,whereas solar radiation and precipitation insignificantly increased.All seasonal temperature significantly increased in the period of1982-2015 while all seasonal solar radiation values insignificantly increased.Except summer precipitation,spring and autumn precipitation insignificantly increased,and summer precipitation insignificantly decreased.Precipitation insignificantly increased during both sub-periods,i.e.1982-2009 and 2010-2015.Solar radiation insignificantly decreased for both time periods.However,temperature significantly increased in the first period and insignificantly increased during the second time period.It can be concluded that the significant increasing of temperature during 1982-2015 is due to significant increase in the first period.3.Attribution of vegetation change.NDVI versus precipitation has significant negative correlation,whereas NDVI versus solar radiation and NDVI versus temperature have significant positive correlation in the period of 1982-2015.In the first period also this correlation phenomenon remained,but negative correlation of NDVI versus precipitation strengthened in the second time period.Positive correlation of NDVI versus solar radiation and NDVI versus temperature also strengthened during the second time period.Multivariate regression analyses released that NDVI mostly dependent on climate variables than human actions.According to analyses based on the developed vegetation-climate equation,climate change dramatically influenced(90%)on vegetation while human activities constituted 10%in Uzbekistan.