Search

The rainfall, one of the most important natural input resource for dryland agricultural production system, is erratic and temporal in nature. An attempt has been made to analyze thirty years (1990-2019) of meteorological data for prediction of probable week of onset and withdrawal of monsoon and to end with crop planning in North Gujarat region (India).The highest and lowest amount of weekly rainfall was observed in 27th and 39th SMW, respectively. The probability distribution functions viz. generalized extreme value, Gumbel maximum, Gamma and Weibull were found best-fit for prediction of weekly rainfall. The analysis revealed 26th SMW (25 Jun – 01 Jul) and onwards as the most suited sowing time of kharif crops. There are also chances of occurrence of moisture stress during 34th and 35th SMW. The results would be useful for agricultural scientists, researchers, decision makers and policy planners in the field of agricultural crop planning and irrigation management for semi arid regions.

This study investigates presence/absence of homogeneity in 32-yr (1981–2012) rainfall record of four individual monsoon months (June–September) and monsoon season (JJAS) for 16 stations in Saraswati River basin, Gujarat, India. Temporal homogeneity is examined by Hartley, Link-Wallace, Bartlett, and Tukey tests, and spatial homogeneity is tested by Levene’s and Tukey tests. Coefficient of variation for rainfall in June (72–163%), July (48–100%), August (78–114%) and September (93–127%) indicate a large variability in comparison to that in JJAS period (45–60%). Correlation coefficient (r) finds moderately significant (r ≥ 0.7) to highly significant (0.7 > r ≥ 0.3) relationships in rainfall for 68 (57%), 120 (100%), 120 (100%), 109 (91%), and 120 (100%) pairs of stations in June, July, August, September, and JJAS, respectively. Distribution of rainfall is uniform and stable in July, and hence, kharif crops may be sown in July to mitigate impact of uncertain rainfall on agriculture. Dissimilar results of four homogeneity tests justify approach of adopting multiple statistical tests. Considering the likely findings of Link–Wallace and Tukey tests, both are recommended for testing homogeneity. Non-homogeneity is found at Paswadal (June, September, and JJAS), Navawas (August and JJAS), Palanpur (JJAS), and Pilucha (September) stations. The Levene’s test reveals spatial homogeneity in July, August, September, and JJAS; and non-homogeneity in June. Hierarchical cluster analysis delineates four clusters of rainfall stations in four months and JJAS with their geographically distinct locations and a remarkable difference in inter-annual rainfall dynamics.

A stochastic model for weekly water deficit series, using 28 years climatological data, under climatic condition of S.K. Nagar has been developed. The turning point test and Kendall’s rank correlation test are applied for detecting the trend. Correlogram technique is used to detect the periodicity, which is then analyzed by Fourier series method. Significant harmonics were also identified. The statistical properties of the generated water deficit series were compared with observed series. The developed model was validated by predicting two years ahead and compared with the observed water deficit series, The test results indicated the high degree of model fitness. The developed model may be used for representing the time-based structure of the water deficit time series.

The frequency analysis of extreme weekly water deficit in different Agro-climatic Zones of Gujarat using the three most common distributions have been computed. ÷2 test for goodness of fit of the observed data to the theoretical distribution was also performed. The distribution that gave the lowest chi-square value has been selected as the best for that location and the predicted maximum weekly water deficit values have been reported.