Evidence of asymmetric change in diurnal temperature range in recent decades over different agro-climatic zones of India

摘要

Diurnal temperature range (DTR) is an important indicator of climatic change and a critical thermal metric to assess the impact on agriculture and human health. This study investigates the seasonal, annual and decadal changes in the spatio-temporal trend in DTR and air temperatures (maximum: T-max and minimum: T-min) during 1951-2016 and solar radiation (Srad) during 1984-2016 over 14 different agro-climatic zones (ACZs) in India. The changes in the DTR trend between two time periods:1951-2016 and 1991-2016 (recent period) are also assessed. The results indicate an overall increasing trend in DTR (0.038 degrees C/decade), T-max (0.078 degrees C/decade, significant), T-min (0.049 degrees C/decade) during 1951-2016 and Srad (0.10 MJ/m(2)/day/decade) during 1984-2016. However, a decreasing trend in DTR (-0.02 degrees C/decade) and a significant increasing trend in T-min (0.210 degrees C/decade) was noted during 1991-2016. The decadal changes showed an evident decline in DTR during the recent period since 1991. The relative increase in T-min (0.21 degrees C/decade, significant) compared to T-max (0.18 degrees C/decade) resulted in a decreasing DTR trend. This was evident across the 5 out of the 14 agro-climatic zones for the 1991-2016 period. The seasonal analysis showed a significant (95%) increasing trend in DTR during pre-monsoon and monsoon (1951-2016), and a negative trend for the post-monsoon and monsoon since 1991. There were also interesting spatial differences found with the ACZs in the north-west, parts of Gangetic plain, north-east, and central India exhibiting negative DTR trends. The effect of Srad is larger on T-max than T-min; therefore, the decrease in Srad in parts of Gangetic plain likely contributed to a smaller increase in T-max relative to T-min and led to a decreasing trend in DTR. At the same time, the west coast, east coast, and southern region show positive trends. The observational analysis finds a distinct increase in the T-min and also highlights the need for future assessments to continue investigate the causes of these spatio-temporal changes found in this study.