Robert Shibatani’s Post

  “Streamflow variability of the Pearl River Basin”   Understanding the spatiotemporal characteristics of streamflow and the complex interactions between atmospheric forcing and land surface properties remains a challenge for river managers across the globe. Fortunately, process-based hydrological models provide a viable solution in many cases to address this challenge.   Streamflow in the Pearl River Basin is highly variable and controlled by complex land surface processes and atmospheric processes over the heterogeneous terrain. Two key factors primarily govern streamflow: 1) location of the active precipitation zone, which is determined by the interaction between the monsoon path and uplifting effect of the terrain, and 2) redistributions resulting from land use and soil characteristics. Distinct patterns in the different water fluxes across the different regions were observed.  The Pearl River Basin is divided into a drought-prone upstream, a hydrologically active midstream, and a typhoon-affected downstream. Specifically, surface flow exhibited the highest activity within the precipitation zone.  Lateral flow and actual evapotranspiration (AET) had the greatest intensity in the forests and in agricultural regions, respectively, and aquifer/phreatic flow was more active in areas with coarser soil textures.     The land surface processes of the AET and aquifer retention significantly govern the temporal variability of the streamflow, contributing to precipitation and streamflow being out of phase in the Pearl River Basin. Full details are provided in Zhang et al. (2024) in Hydrological Processes, “Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts”

The role of a basin's drainage area on its runoff response is generally ignored once the discharge data is area-normalized. Although some studies in the past have highlighted the need to account for drainage area while predicting peak discharge, how discharge is linked to drainage area during very dry periods has not been studied at all. Our perspective on this important but overlooked question is provided here:

🚨 New Post Alert 🚨 This week, Ternikar Chirag Rajendra and Shubham Goswami tell us about using GRACE data and Kalman filters to improve evapotranspiration estimates. Read more about this GRACE application to understand the hydrological cycle here: https://lnkd.in/e_Rw38GJ

A Study of the Homogeneity of Climatic Data for Rain, Temperature and Humidity for Nineveh Governorate Hasan Jamal Al-Bazaz Omar M. A Abstract In recent years, climatic changes have had a greater impact on the hydrological cycle, leading to continuous changes in climate on both temporal and spatial scales. Therefore, this study aimed to verify the credibility and homogeneity of the data, so when conducting any study in the field of climate and hydrological change, the homogeneity of the data used must be tested. In the current study, eight climatic stations distributed in Nineveh Governorate were selected, using climatic data represented by (rainfall, maximum and minimum temperatures, and maximum and minimum humidity) for the time period 1990-2020. Four statistical methods were used, namely, Von Neumann test (VONT), Standard Normal Homogeneity test (SNHT), Buishand test (BRT) and the Pettitt test at a significance level of 5%. The results showed that the monthly rainfall was homogeneous for all stations except for three months (2, 2, 11) for the stations of Tal-Abta, Ba’aj, and Al-Sheikhan. As for the temperature and humidity, they were heterogeneous for most of the stations, as the percentages for months that were heterogeneous in temperature reached 35% and 42% for the maximum and minimum, respectively. As for the humidity, the percentage of the heterogeneous months were 18% and 14% for the maximum and minimum, respectively. The study showed that the SNHT and VON tests are the most sensitive to the breakpoint and the Pettitt test is the least sensitive in most tests. The heterogeneous climatic data were also corrected by using the double mass curve method and converted into homogeneous climatic data. https://lnkd.in/dtqZn7mr

Most hydrological models simulate sub-surface discharge as outflow from lumped reservoirs, relying on Dupit-Boussinesq's hydraulic groundwater theory. This theory assumes hillslopes drain to nearby stream channels only through 'local' sub-surface flow paths, modeling the basin as the sum of its hillslopes. However, our recent study (https://lnkd.in/ddJEMmcU) reveals that deeper 'regional' sub-surface flow paths may dominate at larger scales. We analyzed the scaling relationship between discharge and basin area during both wet and dry periods using a channel network morphology-based model that accounts for regional sub-surface flow paths. Our findings show that the discharge-area scaling exponent increases during extended dry periods, as smaller basins with only local sub-surface discharge dry out faster than larger basins with significant regional sub-surface flow contributions. This study, therefore, provides evidence that a basin cannot be modeled merely as the sum of its hillslopes. Article Link: https://lnkd.in/dtJi9fTy #Research #WaterResources #HydrologicalModeling

Editor's Choice Article for the Jun. 2024 Issue of JHE: "Response of Precipitation Increases to Changes in Atmospheric Moisture and Its Flux in the Columbia River Basin: WRF Model–Based Precipitation Maximization for PMP Studies" by Hiraga et al. US probable maximum precipitation (PMP) estimation assumes changes in precipitable water align with precipitation, but this may not hold true for the Pacific Northwest. This study of atmospheric river events in the Columbia River Basin finds a stronger correlation between integrated water vapor transport changes and precipitation than with precipitable water changes. It underscores the need to consider both atmospheric water vapor and its transport mechanisms for accurate PMP estimation. To read the article, please visit: https://lnkd.in/gdZxcE3z For other Editor's Choice articles, please visit: https://lnkd.in/gJN2fAT #hydrology #watermanagement #extremes #PMP #AR #extremes #floods

“Alaska river ice and Atmospheric Rivers … are they linked?” A recent study investigated the impact Atmospheric Rivers (ARs) and non-AR related precipitation events have on 26 river observation points in Alaska. The effect of ARs on local temperature increases throughout the study domain; the contribution of ARs to precipitation events, including variability and extremes; and fused precipitation, temperature and time, with a heat transfer approximation and correlation analysis were examined to better understand how precipitation events impact river ice breakup timing. In Alaska, ARs account for 40% of total precipitation, explain 47% of precipitation variability, and make up 59% of extreme precipitation events, each year. The results recorded in this investigation are consistent with past works, such as Nash et al. (2024) which showed that throughout southeast Alaska, as few as six annual AR events can account for 68%–91% of precipitation days. Current analysis showed that more frequent and intense precipitation events (including AR events) occurring during the coldest period of the year, appear to delay the annual breakup date of river ice.  However, the results DO NOT show that ARs are unique relative to non-AR forms of precipitation in this regard, as both appear to delay the breakup date. No evidence showed that increased precipitation events of any kind, close to the breakup date, accelerated the river ice breakup date. While this current analysis focused on the major thermodynamic drivers of river ice breakup (i.e., temperature, precipitation and time) which are influenced by large scale systems like ARs, it is important to remember that the hydrological processes (e.g., stream discharge, temperatures, river morphology and inherent watershed characteristics are just as important in evaluating the dynamics of the river ice. For full study details, please see Limber et al. (2024) in GRL, “Influence of Atmospheric Rivers on Alaskan River Ice”

“Long-term groundwater trends in the mountains of Canada and the U.S.” A recent study quantified temporal trends in mountain groundwater levels and explored how various climatic, physiographic and anthropogenic factors are affecting long-term trends. Data from 171 public groundwater observation wells having at least 20 years of monthly data were compiled within mountain regions across Canada and the U.S. In general, the wells that showed stronger declines in groundwater levels were located at lower elevations and with higher annual air temperatures, lower annual precipitation and in sedimentary rock. By contrast, colder mountain settings at higher elevations or with crystalline rock showed more stable or even increasing groundwater levels. Precipitation and temperature trends, and aquifer type also influenced groundwater level trends.  The relationship between groundwater trend and potential explanatory variables is different for different ecoregions across the continent, highlighting the importance of local hydrologic context. Mountains and other cold regions are changing dramatically as our global hydroclimate continues to rapidly shift with cascading effects on water resources. These results provide an early assessment on how mountain groundwater dynamics are changing.  While water managers tend to focus on downstream waterbodies (e.g., estuaries and deltas), a large remaining knowledge gap in the generation of mountain runoff and its water resource implications are being left, relatively unattended. For details, please see Samways et al. (2024) in Hydrological Processes, “Long-term trends in mountain groundwater levels across Canada and the United States”

Why do we calibrate a hydrological model? Catchments across the globe exhibit dissimilarities in terms of soil properties, landscape, and thus hydrological (streamflow) responses. How dissimilar are they? Are there any similarities across all catchments? This study attempts to address these questions. We demonstrate that catchments around the globe show similarities to a great extent requiring no calibration (or calibration with very few parameters) in determining streamflow responses. We showed that climate (rainfall and temperature) contains sufficient information for daily streamflow prediction in ungauged basins. More importantly, this study promotes the idea of developing a climate-centric hydrological model rather than the traditional soil-centric approach. This leads to a hydrological model with few or no parameters. Read the full article here: https://lnkd.in/dFnquiuj (Note: The modified version of the calibration-free Dynamic Budyko model used in this study, which has shown significant improvements, is currently under review.)

Excited to share our latest open-access article in Hydrological Processes! 🌊 We analyzed long-term discharge records from 96 Austrian springs, identifying four distinct categories based on seasonality and autocorrelation. Our study links these patterns to climate and catchment characteristics, offering a reproducible framework that enhances traditional spring classification methods. Curious how this approach can improve hydrological knowledge and sustainable water management? Check it out here: https://lnkd.in/dCzHDQXj #Hydrology #Springs #WaterResources #OpenAccess