Application of the Regression-Augmented Regionalization Approach for BTOP Model in Ungauged Basins

Ten years after the Predictions in Ungauged Basins (PUB) initiative was put forward, known as the post-PUB era (2013 onwards), reducing uncertainty in hydrological prediction in ungauged basins still receives considerable attention. This integration or optimization of the traditional regionalization approaches is an effective way to improve the river discharge simulation in the ungauged basins. In the Jialing River, southwest of China, the regression equations of hydrological model parameters and watershed characteristic factors were firstly established, based on the block-wise use of TOPMODEL (BTOP). This paper explored the application of twelve regionalization approaches that were combined with the spatial proximity, physical similarity, integration similarity, and regression-augmented approach in five ungauged target basins. The results showed that the spatial proximity approach performs best in the river discharge simulation of the studied basins, while the regression-augmented regionalization approach is satisfactory as well, indicating a good potential for the application in ungauged basins. However, for the regression-augmented approach, the number of watershed characteristic factors considered in the regression equation impacts the simulated effect, implying that the determination of optimal watershed characteristic factors set by the model parameter regression equation is a crux for the regression-augmented approach, and the regression strength may also be an influencing factor. These findings provide meaningful information to establish a parametric transfer equation, as well as references for the application in data-sparse regions for the BTOP model. Future research should address the classification of the donor basins under the spatial distance between the reference basin and the target basin, and build regression equations of model parameters adopted to regression-augmented regionalization in each classification group, to further explore this approach’s potential.

Quantitative estimation on contribution of climate changes and watershed characteristic changes to decreasing streamflow in the Huangshui Basin, China

<p>In the past 60 years, climate changes and underlying surface of the watershed have affected the structure and characteristics of water resources to a different degree It is of great significance to investigate main drivers of streamflow change for development, utilization and planning management of water resources in river basins. In this study, the Huangshui Basin, a typical tributary of the upper Yellow River, is used as the research area. Based on the Budyko hypothesis, streamflow and meteorological data from 1958-2017 are used to quantitatively assess the relative contributions of changes in climate and watershed characteristic to streamflow change in research area. The results show that: the streamflow of Huangshui Basin shows an insignificant decreasing trend; the sensitivity coefficients of streamflow to precipitation, potential evapotranspiration and watershed characteristic parameter are 0.5502, -0.1055, and 183.2007, respectively. That is, an increase in precipitation by 1 unit will induce an increase of 0.5502 units in streamflow, and an increase in potential evapotranspiration by 1 unit will induce a decrease of 0.1055 units in streamflow, and an increase in the watershed characteristic parameter by 1 unit will induce a decrease of 183.2007 units in streamflow. Compared with the reference period (1958-1993), the streamflow decreased by 20.48mm (13.59%) during the change period (1994-2017), which can be attribution to watershed characteristic changes (accounting for 73.64%) and climate change (accounting for 24.48%). Watershed characteristic changes exert a dominant influence upon the reduction of streamflow in the Huangshui Basin.</p>

Watershed Prioritization of Kaeng Lawa Sub-Watershed, Khon Kaen Province Using the Morphometric and Land-Use Analysis: A Case Study of Heavy Flooding Caused by Tropical Storm Podul

During 29–31 September 2019, tropical storm Podul moved into the Kaeng Lawa sub-watershed (KLs), the upstream area of the Chi watershed, causing the worst flooding in 40 years. This study was carried out to analyze the watershed characteristic (WC) variables and prioritize the risks of land-use patterns in KLs, Khon Kaen Province, using a watershed delineation approach. As a result of this study, of the 11 sub-watersheds in the Kaeng Lawa watershed, only KL03 and KL04 were deemed medium priority within their drainage and storage capacity systems. KL01, in the upstream sub-watershed, displayed very low priority. The pattern of land-use that appeared most in KL01 sub-watershed was deforestation, where the upper forest area appeared to show a 63% decrease from 2002 to 2017. The decreased forest area was replaced with agricultural area, for crops such as sugarcane and para-rubber, and fruit farms. Moreover, increases in urban area expansion were found in the downstream area in the north of KLs. The findings of this study reveal that severe flooding in this area was caused not only by tropical storm Podul, but also by the low prioritization of watershed characteristics and patterns of land-use that resulted in decreasing forested area in this watershed area. Consequently, these factors have influenced watershed storage and caused an accumulation of water volume, which regularly results in floods. Thus, flood mitigation should be implemented urgently, in the very low priority areas of the study area first.

Alpha Modeling of Nakayasu Synthetic Unit Hydrograph for Part of Watersheds in Indonesia

The lacks of hydrograph data in the field has become the drawback of the hydraulic structure planning. However, such a conditional deficiency in particular, has urgently placed the Synthetic Unit Hydrograph (SUH) models to be very great utility. The Synthetic Unit Hydrograph (SUH) is a popular model that is used in many water resources designs especially in design flood analysis in ungagged watershed. One of the SUH that is usually used in Indonesia is Nakayasu SUH. This model is depended on the α parameter that is influencing the unit hydrograph ordinate and time base. This research intends to build a model of α parameter that is as the characteristic factor of part of watersheds in Indonesia. The methodology consists of observed unit hydrograph analysis for obtaining the α parameter in each watershed, to collect the characteristic data in each watershed, and then to formulate the α parameter model that is as the function of watershed characteristic. The result is formulation model of α that can be used to analyze the design flood in the watershed in Indonesia

The effects of climate and catchment characteristic change on streamflow in a typical tributary of the Yellow River

Hydrological cycle changes that occur due to a changing environment is a hot topic in the field of hydrological science. It is of great practical significance to study the response mechanism of hydrological process change for future water resources planning and management. In this study, the effects of climate and watershed characteristic change on the streamflow in a typical tributary of the Yellow River (the Fen River watershed) are studied based on the Budyko hypothesis. The results show that: the sensitivity coefficients of streamflow to precipitation, potential evapotranspiration, and the watershed characteristic coefficient were 0.1809, −0.0551, and −27.0882, respectively. This meant that a 1 mm decrease in the precipitation would induce a 0.1809 mm decrease in the streamflow. Additionally, a 1 mm decrease in the potential evapotranspiration would induce a 0.0551 mm increase in the streamflow, and an increase of 1 in the watershed characteristic coefficient would induce a 27.0882 mm decrease in the streamflow. The streamflow of the Fen River watershed showed a significant decreasing trend during the reference period (1951–1977). In addition, the streamflow of the change period (1978–2010) decreased 26.87 mm; and this was primarily caused by watershed characteristic change which accounted for 92.27%, while climate change only accounted for 6.50%.

Assessment of Hydrologic Alteration Metrics for Detecting Urbanization Impacts

Urbanization is increasing rapidly and has the potential to alter the hydrologic cycle. It is uncertain if hydrologic alteration metrics developed for large-scale analyses detect the impacts of urbanization. This study tests the ability of two such methods, Indicators of Hydrologic Alteration (IHA) and streamflow signatures, to detect the effects of urbanization in two watersheds in the southeastern U.S.A. A hydrologic model (HEC-HMS) was used to simulate flows in ungauged upstream tributaries to determine if analysis of flow from a large gauged watershed detects urbanization effects on upstream tributaries. IHA analysis detected trends in time in the watersheds, but the results were the opposite of what would be expected as urbanization increased minimum flows, decreased maximum flows, and decreased flashiness based on the trend in time and comparison with an undeveloped watershed. IHA parameters were more sensitive to urbanization than streamflow signatures. Subcatchments that transitioned from low to moderate or high levels of urbanization had greater levels of hydrologic alteration than was detected at the watershed outlet. Analyses of stream gauge network data may underestimate the importance of urbanization as a watershed characteristic due to scale issues, the variable effects of water management, and the dynamic nature of urbanization.

Regional modelling with flood-duration-frequency approach in the middle Cheliff watershed

This study describes a statistical approach of watercourses hydrological regimes in flood, taking into account the latter duration d and return period T. The choice of Middle Cheliff watershed as study area is linked to disasters strong return period in the western region of Algeria. The Midlle Cheliff catchment basin, located in northwest Algeria, has particularly experienced severe floods over the last years. In view of the recurrence of these unusual events, the estimation and the predetermination of floods extreme quantiles are a strategic axis for prevention against floods in this region. The a curves are first of all locally determined, directly from a statistical analysis of flow continuously exceeded during a duration d (QCXd) on different durations from available data of the study region. Then, these curves are compared to those obtained by application of different regional models VFS (Vandenesse, Florac and Soyans) in which two indices of the watershed characteristic flood are taken into account, a descriptive duration of the flood dynamics (D) and the instantaneous maximal annual flow of 10 year return period (QIXA10). The final choice of the model is based on verification of certain criteria, such as: Nash and the root mean squared error (RMSE). The closest regional models to the local ones are Florac’s for low duration and return periods, and Vandenesse’s for large return periods, for different durations. These results could be used to build regional Q-d-F curves on ungauged or partially gauged Algerian basins.