Influence of varied drought types on soil conservation service within the framework of climate change:insights from the Jinghe River Basin,China

Severe soil erosion and drought are the two main factors affecting the ecological security of the Loess Plateau,China.Investigating the influence of drought on soil conservation service is of great importance to regional environmental protection and sustainable development.However,there is little research on the coupling relationship between them.In this study,focusing on the Jinghe River Basin,China as a case study,we conducted a quantitative evaluation on meteorological,hydrological,and agricultural droughts(represented by the Standardized Precipitation Index(SPI),Standardized Runoff Index(SRI),and Standardized Soil Moisture Index(SSMI),respectively)using the Variable Infiltration Capacity(VIC)model,and quantified the soil conservation service using the Revised Universal Soil Loss Equation(RUSLE)in the historical period(2000-2019)and future period(2026-2060)under two Representative Concentration Pathways(RCPs)(RCP4.5 and RCP8.5).We further examined the influence of the three types of drought on soil conservation service at annual and seasonal scales.The NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP)dataset was used to predict and model the hydrometeorological elements in the future period under the RCP4.5 and RCP8.5 scenarios.The results showed that in the historical period,annual-scale meteorological drought exhibited the highest intensity,while seasonal-scale drought was generally weakest in autumn and most severe in summer.Drought intensity of all three types of drought will increase over the next 40 years,with a greater increase under the RCP4.5 scenario than under the RCP8.5 scenario.Furthermore,the intra-annual variation in the drought intensity of the three types of drought becomes smaller under the two future scenarios relative to the historical period(2000-2019).Soil conservation service exhibits a distribution pattern characterized by high levels in the southwest and southeast and lower levels in the north,and this pattern has remained consistent both in the historical and future periods.Over the past 20 years,the intra-annual variation indicated peak soil conservation service in summer and lowest level in winter;the total soil conservation of the Jinghe River Basin displayed an upward trend,with the total soil conservation in 2019 being 1.14 times higher than that in 2000.The most substantial impact on soil conservation service arises from annual-scale meteorological drought,which remains consistent both in the historical and future periods.Additionally,at the seasonal scale,meteorological drought exerts the highest influence on soil conservation service in winter and autumn,particularly under the RCP4.5 and RCP8.5 scenarios.Compared to the historical period,the soil conservation service in the Jinghe River Basin will be significantly more affected by drought in the future period in terms of both the affected area and the magnitude of impact.This study conducted beneficial attempts to evaluate and predict the dynamic characteristics of watershed drought and soil conservation service,as well as the response of soil conservation service to different types of drought.Clarifying the interrelationship between the two is the foundation for achieving sustainable development in a relatively arid and severely eroded area such as the Jinghe River Basin.

Do Forest Landscape Pattern Planning and Optimization Play a Role in Enhancing Soil Conservation Services in Mountain Areas of Western China?

The relationship between landscape patterns and soil conservation,as well as the need for nature-based soil erosion control and landscape pattern optimization,have increasingly gained attention in the scientific and political community in the past decade.With the implementation of a series of afforestation/reforestation projects in the western China,the optimization and management of forest landscape patterns will become more important for soil conservation.In this study,the Bailongjiang Watershed(BLJW),in the western China,was used as a case study to explore the relationship between the forest landscape pattern and soil conservation services using mathematical and spatial statistics methods.A spatially-explicit model called the sediment delivery ratio(SDR)model of the Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)was used to assess the soil conservation service in each sub-basin of BLJW in 1990,2002,and 2014,and landscape indices were used to describe changes in forest landscape patterns in each sub-basin.Nine forest landscape indices,including the percentage of landscape(PLAND),largest patch index(LPI),edge density(ED),landscape shape index(LSI),mean patch shape(SHAPEMN),patch cohesion index(COHESION),landscape division index(DIVISION),splitting index(SPLIT)and aggregation index(AI),were significantly correlated to the soil conservation service.PLAND,AI,LSI and SPLIT of forestland were determined to be the more important landscape indicators.The results also indicated that soil conservation was substantially scale-dependent.The results demonstrated that landscape type diversity greatly affected watershed soil conservation and can be used for forest landscape restoration and management.Furthermore,spatial statistics analysis indicated that the Spatial Lag Model(SLM)was superior to the Ordinary Least Squares(OLS)for soil conservation regressions in 1990 and 2014,while OLS was more appropriate for the regression in 2002.These findings will be useful for enhancing soil conservation and for optimizing mountainous forest landscape patterns for afforestation/reforestation and regional development.Future planning and implementation of ecological restoration should focus more on strategic spatial planning and integrated landscape management with full consideration of future climate,water availability/consumption,hydrological regime,topography,and watershed features,especially on afforestation and revegetation projects in western mountainous China,where the socio-ecological system is fragile and poor.

Using modified Soil Conservation Service curve number method to simulate the role of forest in flood control in the upper reach of the Tingjiang River in China

To improve flood control efficiency and increase urban resilience to flooding,the impacts of forest type change on flood control in the upper reach of the Tingjiang River(URTR) were evaluated by a modified model based on the Soil Conservation Service curve number(SCS-CN) method. Parameters of the model were selected and determined according to the comprehensive analysis of model evaluation indexes. The first simulation of forest reconstruction scenario,namely a coniferous forest covering 59.35km^2 is replaced by a broad-leaved forest showed no significant impact on the flood reduction in the URTR. The second simulation was added with 61.75km^2 bamboo forest replaced by broad-leaved forest,the reduction of flood peak discharge and flood volume could be improved significantly. Specifically,flood peak discharge of 10-year return period event was reduced to 7-year event,and the reduction rate of small flood was 21%-28%. Moreover,the flood volume was reduced by 9%-14% and 18%-35% for moderate floods and small floods,respectively. The resultssuggest that the bamboo forest reconstruction is an effective control solution for small to moderate flood in the URTR,the effect of forest conversion on flood volume is increasingly reduced as the rainfall amount increases to more extreme magnitude. Using a hydrological model with scenarios analysis is an effective simulation approach in investigating the relationship between forest type change and flood control. This method would provide reliable support for flood control and disaster mitigation in mountainous cities.

An insight to calculate soil conservation service

Quantifying soil conservation service is critical for sustainable land management. However, the traditional algo-rithm includes a gap between barren land and real soil erosion (BSERef), and its paradox is that a mass of barrenland rarely exists in ecologically adaptable areas with fertile soils, which might overestimate soil conservationservice. This study suggests a practical algorithm to effectively evaluate soil conservation service of differentecosystems. We propose a new algorithm based on the difference between cropland without control practicesand real soil erosion (CSERef), which is compared with the BSERef algorithm. Our results show that: (1) a nearlyfive times smaller mean soil conservation amount of cropland occurred in the CSERef algorithm (3.76×106 t·yr–1)than in the BSERef algorithm (20.04×106 t·yr–1);(2) land use has higher explanatory power for the spatial dif-ferentiation of soil conservation rate in the CSERef algorithm (15.93% – 46.34%) than in the BSERef algorithm(5.95% – 44.49%). Our results demonstrate that the BSERef algorithm overestimates the soil conservation serviceof cropland in ecologically adaptable areas, whereas the CSERef algorithm can effectively assess the influence ofland use change induced by anthropogenic activities on soil conservation service. Furthermore, we develop anassessment framework in terms of land use classification system following the Chinese Academy of Sciences. Theframework considers that for water bodies, there is no soil conservation service;for non-ecologically adaptable ar-eas (unused land) with vast barren lands and vegetation cover below 5%, the BSERef algorithm is recommended;the CSERef algorithm is suggested to use in ecologically adaptable areas (including woodland, grassland, crop-land and construction land). This assessment framework can provide scientific assistance for decision-makers toformulate strategies for sustainable land management.

Changes in Ecosystem Service of Soil Conservation Between 2000 and 2010 and Its Driving Factors in Southwestern China

Human activities significantly alter ecosystems and their services; however, quantifying the impact of human activities on ecosystems has been a great challenge in ecosystem management. We used the Universal Soil Loss Equation and county-level socioeconomic data to assess the changes in the ecosystem service of soil conservation between 2000 and 2010, and to analyze its spatial characteristics and driving factors in the southwestern China. The results showed that cropland in the southwestern China decreased by 3.74%, while urban land, forest, and grassland areas increased by 46.78%, 0.86%, and 1.12%, respectively. The soil conservation increased by 1.88 × 10^(11) kg, with deterioration only in some local areas. The improved and the degraded areas accounted for 6.41% and 2.44% of the total land area, respectively. Implementation of the Sloping Land Conversion Program and urbanization explained 57.80% and 23.90% of the variation in the soil conservation change, respectively, and were found to be the main factors enhancing soil conservation. The 2008 Wenchuan earthquake was one of the factors that led to the degradation of soil conservation. Furthermore, industrial adjustment, by increasing shares of Industry and Service and reducing those of Agriculture, has also promoted soil conservation. Our results quantitatively showed and emphasized the contributions to soil conservation improvement made by implementing ecological restoration programs and promoting urbanization. Consequently, these results provide basic information to improve our understanding of the effects of ecological restoration programs, and help guide future sustainable urban development and regional industrial restructuring.

Inference of Reference Conditions for Nutrient Concentrations of Chaohu Lake Based on Model Extrapolation

In the mid-eastern China,there are few or no lakes which are in the absence of anthropogenic disturbances,or their sediments remain undisturbed.As a result,the reference lakes distribution and paleolimnological reconstruction approaches usually are inappropriate to estimate lake reference conditions for nutrients.This yields the necessity of using the extrapolation methods to estimate the lake reference conditions for nutrients within those regions.The lake reference conditions for nutrients could be inferred inversely from the law of mass conservation,current lake nutrient concentration,and the loadings from watershed.Considering the scarcity of hydrological and water quality data associated with lakes and watersheds in China,as well as the low requirement of the watershed nutrient loadings models for these data,the soil conservation service(SCS) distributed hydrological model and the universal soil loss equation(USLE) were applied.The SCS model simulates the runoff process of the watershed,thereby calculating dissolved nutrients annually.The USLE estimates the soil erosion and particulate nutrients annually in a watershed.Then,with the loadings from atmospheric deposition and point source,the previous annual average nutrient concentrations could be acquired given the current nutrient concentrations in a lake.Therefore,the nutrient reference conditions minimally impacted by human activities could be estimated.Based on the proposed model,the reference conditions for total nitrogen and total phosphorus of Chaohu Lake,Anhui Province,China are 0.031 mg/L and 0.640 mg/L,respectively.The proposed reference conditions estimation model is of clear physical concept,and less data required.Thus,the proposed approach can be used in other lakes with similar circumstances.

Energy potential assessment and techno-economic analysis of micro hydro-photovoltaic hybrid system in Goda Warke village,Ethiopia

Rural Ethiopia has significant untapped potential for hydro and solar energy generation systems.However,challenges arise from seasonal variations and unfavourable topographic positions of flowing rivers,hindering the efficient exploitation of these resources.Despite the country’s abundance in hydro and solar energy resources,>75%of the population still lack access to electricity from the national grid.This work deals with energy resource potential assessment and techno-economic analysis of micro hydro-photovol-taic(PV)hybrid systems,considered in the case study of Goda Warke village,located in the Yaya Gulele district.A novel framework is proposed that utilizes the Natural Resource Soil Conservation Service curve number method to assess the energy potential of micro-hydro energy in ungauged basins,specifically at the exit point of the Girar River basin catchment.The average monthly flow rate in the basin is 0.975 m3/s,while the area exhibits a solar radiation potential of 5.39 kWh/m^(2)/day.Energy policy promotes expanding ac-cess to modern energy sources and utilization of indigenous energy resources.Simulation results indicate that the hydro/PV/diesel generator(DG)/battery and hydro/PV/battery systems are the most optimal choices based on net present cost,with the inclusion of a DG for economic comparison.Micro-hydro energy covers most of the electric load in the area,achieving a capacity factor of 47.5%.The cost of energy and net present cost were found to be sensitive to variables such as the price of diesel fuel,pipe head loss,and the growth of the village load.The optimized system demonstrated a hydro energy potential of 1405.37 MWh/year and a PV energy output of 274.04 MWh/year,resulting in a levelized cost of energy of 0.0057 and 0.049$/kWh for the hydro and PV components,respectively.

The quality attribute of watershed ecosystem is more important than the landscape attribute in controlling erosion of red soil in southern China

Landscape and quality attributes are major ecosystem characteristics closely associated with soil conservation service(SCS).However,the intrinsic mechanisms by which these two attributes influence SCS are still unclear.Therefore,this study quantitatively analyzed the landscape pattern,ecological quality,and SCS in the Lianshui River watershed(a typical soil and water loss area of red soil in southern China)and its sub-watersheds in 2019.The boosted regression tree model was used to explore the influence of 15 factors(i.e.,landscape and quality attributes)on SCS at the sub-watershed scale.According to the results,compared with the landscape attribute,the quality attribute of the watershed ecosystem could better explain the spatial heterogeneity of SCS across 66 sub-watersheds.The overall degree of influence of five quality factors on SCS reached 57.81%,with the highest being the normalized differential build-up and bare soil index(NDBSI),at 25.11%.Among 10 landscape factors,aggregation had the greatest influence on SCS,at 28.64%.The relationships between key influencing factors and SCS were nonmonotonic and non-linear,with threshold effects.For example,NDBSI values of 0.18e0.41 had a positive influence on SCS,while NDBSI values of 0.41e0.65 had a negative influence on SCS.The findings broaden our understanding of the response of SCS to changes in landscape and quality attributes at the sub-watershed scale,and could offer comprehensive support for soil erosion management in the watershed ecosystem.