Bramha Dutt Vishwakarma

arXiv2025

Accounting for shelf width in selecting altimetry observations for coastal sea level variability improves its agreement with tide gauges

A novel dynamically varying search radius algorithm is developed that takes advantage of bathymetry information to choose satellite observations that represent coastal sea level variability better. The algorithm is successfully tested at 155 tide gauge stations around the globe and demonstrates broader applicability across different coastal regimes compared to existing validation methods. This is supported by consistently higher median correlation and lower median Normalized Root Mean Square Error (NRMSE). Furthermore, the new algorithm improves the efficacy of the low-resolution product, X-TRACK SLA L2P v2022 (XTRACK), and makes it comparable to the high-resolution (20Hz) coastal products: Along-track sea level anomalies and trends v2.3. Using the algorithm at over 267 stations, XTRACK data shows improved agreement with tide gauges for both linear and non-linear trends. In some regions, such as tidally-dominated estuaries and the Eastern Australian coast, lower correlation and higher RMSE for residual signals are reported, which are discussed.

physics.ao-ph↗

arXiv2023

ET-WB: water balance-based estimations of terrestrial evaporation over global land and major global basins

The prevailing approaches for ET retrievals are either limited in spatiotemporal coverage or largely influenced by choice of input data or simplified model physics, or a combination thereof. Here, using an independent mass conservation approach, we develop water balance-based ET datasets (ET-WB) for the global land and the selected 168 major river basins. We generate 4669 probabilistic unique combinations of the ET-WB leveraging multi-source datasets (23 precipitation, 29 runoff, and 7 storage change datasets) from satellite products, in-situ measurements, reanalysis, and hydrological simulations. We compare our results with the four auxiliary global ET datasets and previous regional studies, followed by a rigorous discussion of the uncertainties, their possible sources, and potential ways to constrain them. The seasonal cycle of global ET-WB possesses a unimodal distribution with the highest (median value: 65.61 mm/month) and lowest (median value: 36.11 mm/month) values in July and January, respectively, with the spread range of roughly +/-10 mm/month from different subsets of the ensemble. Auxiliary ET products illustrate similar intra-annual characteristics with some over/under-estimation, which are completely within the range of the ET-WB ensemble. We found a gradual increase in global ET-WB from 2003 to 2010 and a subsequent decrease during 2010-2015, followed by a sharper reduction in the remaining years primarily attributed to the varying precipitation. Multiple statistical metrics show reasonably good accuracy of monthly ET-WB (e.g., a relative bias of +/-20%) in most river basins, which ameliorates at annual scales. The long-term mean annual ET-WB varies within 500-600 mm/yr and is consistent with the for auxiliary ET products (543-569 mm/yr). Observed trend estimates, though regionally divergent, are evidence of the increasing ET in a warming climate.

physics.ao-ph↗