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Analysis of trend in temperature and rainfall time series of an Indian arid region: comparative evaluation of salient techniques

Machiwal, Deepesh, Gupta, Ankit, Jha, Madan Kumar, Kamble, Trupti
Theoretical and applied climatology 2019 v.136 no.1-2 pp. 301-320
arid zones, autocorrelation, monsoon season, rain, temperature, time series analysis, winter, India
This study investigated trends in 35 years (1979–2013) temperature (maximum, Tₘₐₓ and minimum, Tₘᵢₙ) and rainfall at annual and seasonal (pre-monsoon, monsoon, post-monsoon, and winter) scales for 31 grid points in a coastal arid region of India. Box-whisker plots of annual temperature and rainfall time series depict systematic spatial gradients. Trends were examined by applying eight tests, such as Kendall rank correlation (KRC), Spearman rank order correlation (SROC), Mann-Kendall (MK), four modified MK tests, and innovative trend analysis (ITA). Trend magnitudes were quantified by Sen’s slope estimator, and a new method was adopted to assess the significance of linear trends in MK-test statistics. It was found that the significant serial correlation is prominent in the annual and post-monsoon Tₘₐₓ and Tₘᵢₙ, and pre-monsoon Tₘᵢₙ. The KRC and MK tests yielded similar results in close resemblance with the SROC test. The performance of two modified MK tests considering variance-correction approaches was found superior to the KRC, MK, modified MK with pre-whitening, and ITA tests. The performance of original MK test is poor due to the presence of serial correlation, whereas the ITA method is over-sensitive in identifying trends. Significantly increasing trends are more prominent in Tₘᵢₙ than Tₘₐₓ. Further, both the annual and monsoon rainfall time series have a significantly increasing trend of 9 mm year⁻¹. The sequential significance of linear trend in MK test-statistics is very strong (R² ≥ 0.90) in the annual and pre-monsoon Tₘᵢₙ (90% grid points), and strong (R² ≥ 0.75) in monsoon Tₘₐₓ (68% grid points), monsoon, post-monsoon, and winter Tₘᵢₙ (respectively 65, 55, and 48% grid points), as well as in the annual and monsoon rainfalls (respectively 68 and 61% grid points). Finally, this study recommends use of variance-corrected MK test for the precise identification of trends. It is emphasized that the rising Tₘₐₓ may hamper crop growth due to enhanced metabolic-activities and shortened crop-duration. Likewise, increased Tₘᵢₙ may result in lesser crop and biomass yields owing to the increased respiration.