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Climate indices and drought characteristics in the river catchments of Western Ghats of India

Shetty Swathi, Umesh Pruthviraj, Shetty Amba

Acta Geophysica

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2024

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Vol. 72, no. 1

371--384

EN

The study addresses the long-term trend in rainfall, minimum and maximum temperature, and the climate indices for the river catchments located in the diverse climate of the Western Ghats of India. The dry sub-humid Chaliyar catchment and humid Kajvi catchment have shown a dramatic change in the decadal rainfall, with the decade 1950-1960 being the point of change. The monsoon rainfall has decreased in the Chaliyar and Netravati catchments and increased insignificantly in the Kajvi catchment. With the increase in mean temperature, the number of rainy days is decreasing, and intense rainfall is increasing in the pre-monsoon. The increase in minimum temperature is more severe in all three catchments, irrespective of the region’s climate. The decline in rainy days is more figurative in the humid and per-humid catchments and has seen a 16-20% decrease in Rx 1 day, Rx 3 day, and Rx 5 day in the past six decades with an insignificant increase in the dry subhumid catchment. The frightful increase in warm days/nights with a decrease in cool days/nights has been alarming for the extremity of temperature in future years. The significant changes in the forest area in Chaliyar and Kajvi catchment and the increase in a built-up area in Netravati may have a decisive role in the nonseasonal variability in rainfall and temperature along with increasing greenhouse gases. In the case of meteorological drought studied using the Standardized Precipitation Index (SPI), moderate droughts have occurred over the Chaliyar and Kajvi, and extreme droughts over the Netravati catchments with no reduction in the frequency or severity of short-duration extreme rainfall events. The geographical location of the catchment has a greater impact on the characteristics of the rainfall and meteorological drought, and these changes in the hydrological regimes of the catchment have a significant bearing on the water availability in the catchments in the future years.

2

Satellite ET-based irrigation performance : Strategies to increase rainfed crops production in the lower Baro watershed, Ethiopia

Befikadu Deneke Fiseha, Shetty Amba, Fufa Fekadu

Journal of Water and Land Development

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2023

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no. 58

53--61

EN

Satellite-based irrigation performance is a valuable tool for improving yields in irrigated areas across the world and requires adequate land for long-term development. This study aimed to increase irrigation performance and yield gap variation of rainfed crops using the database of FAO’s Water Productivity Open Access Portal (WaPOR) and the Global Yield Gap Atlas. The evapotranspiration (ET) performance of irrigation is expressed in equity (CV of ET), reliability, adequacy (CV of ET), and water productivity (kg∙m-3). The rainfed crops are interpreted in terms of metric tonnes/ha. Specifically, 20,325 km2 of suitable pastoral land across eight sub-classes was converted to rainfed rice, sugarcane, maize, and vegetable crops. Results showed that the R2 value was 0.97 at Baro Itang and -0.99 at Sor Metu, with the Baro Gambella sub-catchment having the largest yield gap of 4.435.2, 8.870.4, and 10.080∙106 kg when the yield increased by 1/3, 2/3, and 3/4. On the other hand, Gumero Gore had the smallest yield gap of 10,690, 29,700, and 33,750 kg, respectively. The management regime was 2.87, 0.87, and 0.35 kg∙m-3 for growers in the estate, farmer association, and individual, respectively. The study concludes that no single irrigation technique can be considered the best, and a thorough analysis of spatiotemporal variation of the irrigation performance indicators and the yield gap in the water-scarce lower Baro watershed is required.

3

Assessment of surface soil moisture from ALOS PALSAR 2 in small scale maize felds using polarimetric decomposition technique

Gururaj Punithraj, Umesh Pruthviraj, Shetty Amba

Acta Geophysica

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2021

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Vol. 69, no. 2

579--588

EN

Surface soil moisture knowledge is important, especially in agriculture and irrigation management. Properties of microwave remote sensing like penetration power and longer wavelength facilitate retrieval of surface soil moisture. ALOS PALSAR-2, quad polarized data are used to retrieve surface soil moisture using polarization decomposition techniques in a marginal farmer small-scale maize feld. The focus of the study is to explore the utility of ALOS PALSAR-2 in retrieving surface soil moisture using the polarization decomposition technique. The demonstration of the study is carried out in Malavalli village, southern India, an agricultural predominant area. The study involves feld soil moisture sampling in synchronous with satellite pass, measuring soil properties, preprocessing of SAR data, polarization decomposition, proportional analysis, regression analysis, model calibration and validation. Van Zyl decomposition gave the highest surface scattering component (43%) and reduced volumetric scattering component compared to Yamaguchi and Freeman–Durden decomposition. Surface scattering component of Yamaguchi decomposition gave a good coefcient of determination (R2=0.8029) with feld-measured surface soil moisture. The semi-empirical model (SEM) was developed using surface scattering component and depolarization ratio with adjusted R2=0.75 at 95% confdence interval. On its comparison with existing soil moisture models, it is observed that the developed model is performing well with RMSE and AEmax of 1.81 and 2.88, respectively. Implying the applicability of ALOS PALSAR-2 in soil moisture retrieval in marginal farmer small-scale maize felds gave satisfactory results of accuracy.

4

Multi variable calibration of hydrological model in the upper Omo Gibe basin, Ethiopia

Nesru Mudesir, Shetty Amba, Nagaraj M. K.

Acta Geophysica

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2020

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Vol. 68, no. 2

537--551

EN

The calibration of any hydrological model in any river basin is generally performed using a single hydrological variable. Spatially distributed hydrological modeling provides an opportunity to enhance the use of multi-variable calibration models. The objective of this study is to test the efciency of satellite-based actual evapotranspiration in the HBV hydrological model to render the catchment water balance using multi-variable calibration in the upper Omo-Gibe basin in Ethiopia. Five years (2000–2004) meteorological data, streamfow, and actual evapotranspiration (ETa) based on remote sensing were used for calibration and validation purposes. The performance of the HBV model and the efciency of SEBS–ETa were evaluated using certain calibration criteria (objective function). The model is frst calibrated using only streamfow data to test HBV model performance and then calibrated using a multi-variable (streamfow and ETa) dataset to evaluate the efciency of SEBS–ETa. Both model setups were validated in a multi-variable evaluation using streamfow and ETa data. In the frst case, the model performed well enough for streamfow and poor for ETa, while in the latter case, the performance efciency of SEBS–ETa and streamfow data shows satisfactory to good. This implies that the performance of hydrological models is enhanced by employing multi-variable calibration.