The Impact of Reforestation Induced Land Cover Change (1990–2017) on Flood Peak Discharge Using HEC-HMS Hydrological Model and Satellite Observations: A Study in Two Mountain Basins, China

Optimizing spatial patterns of ecosystem services in the Chang-Ji-Tu region (China) through Bayesian Belief Network and multi-scenario land use simulation

To foster an ecological civilization and ensure sustainable development of population resources, a critical focus of China's land spatial planning initiatives is the complex interplay among the prudent utilization of regional natural resources, stable socio-economic growth, and ecological environment preservation and governance. This interplay is vital for improving the population's quality of life, enhancing national resilience, and fostering the development of an ecological civilization. Within this context, this research focuses on the Chang-Ji-Tu region, employing a hybrid InVEST-Bayesian Belief Network-PLUS model. This approach facilitates a comprehensive assessment of habitat quality (HQ), carbon sequestration (CS), soil conservation (SC), crop production (CP), and total ecosystem services (TES) spanning 2005 to 2020, to optimize spatial structures based on these assessments. The findings indicate significant insights: (1) temporally, both HQ and CS exhibit an initial ascent followed by a subsequent decline, while SC demonstrates a rise, subsequent decrease, and then a gradual increase. CP shows a consistent increase, and TES initially decreases before experiencing a rise. Spatially, regions exhibiting high CP are primarily located in the northwest, in contrast to the southeast, demonstrating lower values. Conversely, HQ, CS, and SC exhibit lower values in the northwest and higher values in the southeast. TES exhibits considerable variability in the northwest and a more equilibrated distribution in the southeast. (2) A positive correlation is observed between land use/cover changes (LUCC) and HQ, CS, and SC, while a negative correlation is noted with CP and TES. (3) In exploring potential scenarios for economic development (ED), natural development (ND), and ecological protection (EP) in 2035, our study categorizes TES into distinct zones: ecological protection prohibited zones, ecological buffer prohibited zones, construction and development suitable zones, and restricted zones for arable land protection. This study, grounded in the current ecosystem status, thoroughly analyzes spatial structural optimization, offering crucial insights for future land spatial planning and ecological restoration.

Coupled hydrodynamic modelling approach to assess land use change induced flood characteristics

MIKE 11 rainfall-runoff model and MIKE 21 overland flow model were successfully coupled in the MIKE FLOOD platform for flood simulation in Gin catchment (932 km²) of Sri Lanka to assess land use change induced changes in flood discharge. MIKE 11 Nedbør-Afstrømings-Model (NAM) rainfall-runoff simulation depicted a good agreement with the observed discharge at Thawalama and Baddegama gauging stations. MIKE FLOOD, validated against the two major flood events that occurred in May 2003 and in May 2017, showed a reasonable agreement with the observed water depths and peak discharge values displaying more than 70% goodness of fit between the observed and simulated inundated extents. Dominant land use change processes in the catchment between 1999 and 2016 were identified as the forest area and built-up land expansion at the expense of agricultural land and bare land which possessed contradictory impacts on flood generation. The impact of a single factor, 17-year land use change, on flood formation was differentiated. In the upstream sub-catchment having 490 km², despite a 0.74% increase in the built-up land, 2.85% increase in the forest area had significantly contributed to mitigate the overall flood formation with 34% and 40% reduction in the peak discharge and the flood volume, respectively. Overall reduction of the flood discharge attributed to the forest expansion emphasised the importance of preserving forest cover and pervious area. The modelling framework presented in this typical tropical monsoon catchment study could be effectively used to quantify the land use change induced flow regime variations in similar catchments.

Evaluation and Improvement of FY-4A AGRI Quantitative Precipitation Estimation for Summer Precipitation over Complex Topography of Western China

Satellite quantitative precipitation estimation (QPE) can make up for the insufficiency of ground observations for monitoring precipitation. Using an Advanced Geosynchronous Radiation Imager (AGRI) on the FengYun-4A (FY-4A) satellite and rain gauges (RGs) for observations in the summer of 2020. The existing QPE of the FY-4A was evaluated and found to present poor accuracy over the complex topography of Western China. Therefore, to improve the existing QPE, first, cloud classification thresholds for the FY-4A were established with the dynamic clustering method to identify convective clouds. These thresholds consist of the brightness temperatures (TBs) of FY-4A water vapor and infrared channels, and their TB difference. Then, quantitative cloud growth rate correction factors were introduced to improve the QPE of the convective-stratiform technique. This was achieved using TB hourly variation rates of long-wave infrared channel 12, which is able to characterize the evolution of clouds. Finally, the dynamic time integration method was designed to solve the inconsistent time matching between the FY-4A and RGs. Consequently, the QPE accuracy of the FY-4A was improved. Compared with the existing QPE of the FY-4A, the correlation coefficient between the improved QPE of the FY-4A and the RG hourly precipitation increased from 0.208 to 0.492, with the mean relative error and root mean squared error decreasing from −47.4% and 13.78 mm to 8.3% and 10.04 mm, respectively. However, the correlation coefficient is not sufficiently high; thus, the algorithm needs to be further studied and improved.

Assessing Hydrological Impact of Forested Area Change: A Remote Sensing Case Study

The interaction between precipitation and vegetation plays a significant role in the formation of runoff, and it is still a widely discussed issue in hydrology. The difficulty lies in estimating the degree to which a forest influences runoff generation, especially flood peaks, on the one hand, due to the small amount of information regarding the evolution of the forest area and density, and, on the other hand, the correlations between these indicators and the runoff and precipitation values. The analysis focuses on a small basin in the mountain region of Romania, the upper basin of the Ruscova River located in northwestern Romania. In this river basin, there is no significant anthropic influence, other than the intense deforestation and reforestation actions. Using satellite images captured by Landsat missions 5, 7 and 8 for the period 1985–2019, the forest canopy density vegetation index was extracted. Using a gridded precipitation dataset, a hydrological model was calibrated based on three scenarios to assess the impact of forest vegetation on the runoff. Analysis of the results of these models conducted on scenarios allowed us to deduce a simple equation for estimating the influence of forest area on maximum river flows. The analysis showed that even small differences in the forest surface area exert an influence on the peak flow, varying between −5.28% and 8.09%.

Precipitation Characteristics of an Abrupt Heavy Rainfall Event over the Complex Terrain of Southwest China Observed by the FY-4A Satellite and Doppler Weather Radar

On 22 July 2019, mesoscale convective systems (MCSs) with an abrupt heavy rainfall event (AHRE) hit Shuicheng County of Guizhou Province in Southwest China causing landslide and debris flow secondary disasters. The AHRE over the complex terrain of Shuicheng County had differences in location and intensity during two stages of the event. The two stages could be divided into different rainfall types (topographic rainfall and synoptic-weather-related rainfall) according to the spatiotemporal distribution and organization of MCSs based on surface and midlevel environmental field conditions. During the topographic rainfall stage, smaller meso-γ-scale (2–20 km) convective cells with lower echo-top heights (6–10 km) occurred along the windward slope of the primary mountain peak. During the synoptic-weather-related rainfall stage, a meso-β-scale (20–200 km) convective echo band with higher echo-top heights (10–14 km) occurred in the valley of the region. An adverse wind area (AWA) with distinct convergence of radar radial velocity existed over Shuicheng County. A formation mechanism analysis of the AHRE showed that topographic rainfall occurred in the warm and moist area, while synoptic-weather-related rainfall occurred due to local convergence and the intrusion of a cold tongue. Compared to the early stage, the cold tongue from the higher terrain superimposed over the warm sector at the base of major mountain ranges appeared to strengthen the rainfall.