Strong Rainfall Events Research Articles

Assessment Of The Existing And Proposed Dike System Along The Cabulig River In Lower Jasaan, Misamis Oriental, Philippines

Abstract. The issue of flooding in the town of Jasaan in Misamis Oriental province poses a threat to 42% of the population. This is more worrisome during the rainy season, especially in the months of October and December were typhoons are at their strongest and passes in proximity to Mindanao island. Residents have reported significant damage to their properties due to flooding, and typhoons like Super Typhoon Odette in December 2021 have worsened the situation when it brought rain while the dike system was dilapedated. The dike systems in the area have been damaged by these natural disasters, and the lack of repair has made the situation worse. Flood hazard mitigation measures have since been implemented. With the frequent occurrence of flooding in the Cabulig River, a validated model is needed to investigate the behavior of the river during strong and significant rainfall events while taking into consideration the current state of the existing dike systems by coupling the modelling systems HEC-HMS and HEC-RAS. Data from the USGS, DOST-PAGASA, DPWH, and Landsat 8 have been used in this study. The results of the Flood Inundation Analysis showed that most of the flooded areas in Barangay Lower Jasaan and Bobontugan are urban areas which exacerbates during heavy rain events. The results of the simulations of the researchers' proposed dike structures shows that it should be extended towards the upstream direction and a minimum dike height of 2.5m is needed with no discontinuities. A 2.5m high dike on the Bobontugan side should also be placed.

Exploring the integration of InSAR data into climate‐driven creep models to assess slow‐moving landslide dynamics

AbstractThe deformation behavior of slow‐moving large landslides is often governed by rainfall characteristics. Based on observational data such as precipitation, deformation measurement, and pore water pressure measurements in the slip zone, in many cases a strong correlation between strong rainfall events, a time‐delayed increase of pore water pressures in the slip zone, and, simultaneously to this, an increase of the deformation rate of the landslide can be found. Based on such detailed data, calculation models, which couples the relation between rainfall characteristics and the development of pore water pressures in the slip zone on one hand and the deformation behavior of the slope on the other, can be developed and be used for a better understanding and a prediction of deformation behavior of such slow‐moving landslides. Climate change issues will lead to a change in rainfall frequency and magnitude and annual temperature distribution characteristics in several regions worldwide, which will also lead to changes in the deformation behavior of such large landslides. In this contribution, satellite‐based interferometric synthetic aperture radar (InSAR) data are discussed to be used as source for deformation measurements as bases for prediction models describing the rainfall‐triggered deformation behavior of slow‐moving landslides.

Assessing landslide damming susceptibility in Central Asia

Abstract. Central Asia regions are characterized by active tectonics, high mountain chains with extreme topography with glaciers, and strong seasonal rainfall events. These key predisposing factors make large landslides a serious natural threat in the area, causing several casualties every year. The mountain crests are divided by wide lenticular or narrow, linear intermountain tectonic depressions, which are incised by many of the most important Central Asia rivers and are also subject to major seasonal river flood hazard. This multi-hazard combination is a source of potential damming scenarios, which can bring cascading effects with devastating consequences for the surrounding settlements and population. Different hazards can only be managed with a multi-hazard approach coherent within the different countries, as suggested by the requirements of the Sendai Framework for Disaster Risk Reduction. This work was carried out within the framework of the Strengthening Financial Resilience and Accelerating Risk Reduction in Central Asia (SFRARR) project as part of a multi-hazard approach with the aim of providing a damming susceptibility analysis at a regional scale for Central Asia. To achieve this, a semi-automated GIS-based mapping method, centered on a bivariate correlation of morphometric parameters defined by a morphological index, originally designed to assess the damming susceptibility at basin/regional scale, was modified to be adopted nationwide and applied to spatially assess the obstruction of the river network in Central Asia for mapped and newly formed landslides. The proposed methodology represents an improvement to the previously designed methodology, requiring a smaller amount of data, bringing new preliminary information on damming hazard management and risk reduction, and identifying the most critical area within the Central Asia regions.

On the development and analysis of coupled surface–subsurface models of catchments. Part 2. A three-dimensional benchmark model and its properties

The objective of this three-part work is to formulate and rigorously analyse a number of reduced mathematical models that are nevertheless capable of describing the hydrology at the scale of a river basin (i.e. catchment). Coupled surface and subsurface flows are considered. In this second part, we construct a benchmark catchment scenario and investigate the effects of parameters within their typical ranges. Previous research on coupled surface–subsurface models have focused on numerical simulations of site-specific catchments. Here, our focus is broad, emphasising the study of general solutions to the mathematical models, and their dependencies on dimensionless parameters. This study provides a foundation based on the examination of a geometrically simple three-dimensional benchmark scenario. We develop a non-dimensional coupled surface–subsurface model and extract the key dimensionless parameters. Asymptotic methods demonstrate under what conditions the model can be reduced to a two-dimensional form, where the principal groundwater and overland flows occur in the hillslope direction. Numerical solutions provide guidance on the validity of such reductions, and demonstrate the parametric dependencies corresponding to a strong rainfall event.

The Development of an ‘Incidental’ Form of Aquaculture During the Late Old Kingdom? Cattle as ‘Marshland Modifiers’ of the Nilotic Marshes and Their Potential Impact upon Old Kingdom Fishing Behaviors

Abstract During the latter half of the Old Kingdom, Egypt experienced irregular water supply. Lower than normal inundations resulted in nutrients normally lost from the river remaining within it. Over the same time, unusually strong rainfall events occurred, transferring even more nutrients into the river. These excess nutrients changed the ecology, affecting the local environment. These changes may have influenced the ecological characteristics of the riverine habitat, and how society responded and adapted. In the latter half of the Old Kingdom, depictions of cattle fording increased, suggesting that cattle were able to take advantage of the plants that now flourished upon the riverbanks as a result of the excess nutrients available. As the movement of cattle across the various river channels increased, the physical structures of the marshlands changed, which may have impacted upon those organisms also exploiting those areas, and affected fishing practices therein. Were these responses accidental, incidental, or co-incidental?

Probabilistic Intraday Wastewater Treatment Plant Inflow Forecast Utilizing Rain Forecast Data and Sewer Network Sensor Data

AbstractForecasting of wastewater treatment plant inflow dynamics constitutes an enabler technology for wastewater treatment process optimization using model predictive control. However, accurate inflow prediction is still challenging, especially for strong rainfall events, where complex system dynamics and missing information on future rainfall represent limiting factors. We propose a seasonal probabilistic time series model for modeling the short‐term wastewater inflow accurately while providing quantification of forecast uncertainty. To ensure suitability for practical implementation, the unconstrained parameters of the predictive distribution are modeled as linear functions of the input variables in the framework of Generalized Additive Models for Location Scale and Shape. Non‐linear effects are approximated by Rectified Linear Units, accounting for buffering within the sewer network and flow‐dependent catchment response time. In addition to water level measurements from within the sewer network and rain rate measurements, rain forecasts are incorporated as exogenous regressors, where historical rain forecasts are used for model calibration. The model performance is evaluated on historical data from a German wastewater treatment plant using deterministic and probabilistic scoring rules. We benchmark against an autoregressive time series model and a long short‐term memory artificial neural network. Our results show that the proposed model unites the benefits of high prediction accuracy of the neural network and enhanced intelligibility of the autoregressive model, but accurate real‐time rain forecasts are mandatory for successful real‐world implementation.

Trends and patterns of polycyclic aromatic hydrocarbons (PAHs) in forest fire-affected soils and water mediums with implications on human health risk assessment

Forest fires are extreme natural/artificial events releasing polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic. Most of the released PAHs are trapped in burnt ash, a part of which is transported and settle on different mediums like soil and water. After strong rainfall events, PAHs enter into surface water bodies through surface runoff, thereby deteriorating water quality. Changes in PAHs levels during the post-fire duration and human health risks due to PAHs released from forest fires need attention. This study aim to explain the trends and patterns of PAHs and health risks due to exposure to soil and water contaminated with PAHs. Forest fires release a higher percentage of low molecular weight PAHs (LMW PAHs) than high molecular weight PAHs (HMW PAHs). Ash and burnt soils contain a higher percentage of LMW PAHs since biomass burning releases huge amounts of LMW PAHs. Whereas, sediments contain a higher percentage of HMW PAHs since most of the LMW PAHs are already degraded. HMW PAHs were causing higher risk to humans (both cancer and non-cancer) due to their higher oxidation potential. Exposure to water contaminated by PAHs resulted in higher health risks for both BaP equivalent and a mixture of PAHs. Exposure to sediment produced the highest health risk due to a higher percentage of HMW PAHs, followed by surface water, burnt soil, ash, and unburnt soil. Cancer and non-cancer risk due to dermal exposure was more elevated than oral exposure. The mixture of PAHs in sediment produced a higher average dermal risk for children (2.21E+00 for cancer and 7.69E+03 for non-cancer risk) and oral cancer risk for adults (7.11E-03). However, exposure to BaP equivalent in sediment produced higher oral non-cancer risk (7.01E+02) for children. Thus, effective PAHs monitoring is required in both soil and surface water mediums for ensuring proper treatment in water supply systems.

Capacitating Strategies to Promote Climate Resilient Coconut-based Farming Systems (CR-CBFS) in Vulnerable Coconut Communities of the Philippines

Climate extremes that continuously bring unpredictable weather patterns particularly strong typhoons and rainfall events devastated many coconut-producing areas in the Philippines. These weather patterns affected the livelihood of farmers and the whole supply chain of the coconut industry. Adoption of a clustering system of farmers is a key approach to sustaining the growing needs of the coconut industry. This will ensure the continuous engagement of farmers in coconut farming where good agricultural practices are performed in developing products that meet the domestic and international market standards. However, clustering of climate-resilient integrated farming systems through participation in multi-purpose cooperatives requires scientific guidance, market-driven production and market linkages.This paper integrates learnings from past coconut and coconut-based farming system (CBFS) projects. Further, it highlights the learning-by-doing approach where core trainers are developed to train farmer groups in designing location-specific climate-resilient CBFS using a hybrid curriculum of CR – Farmers Field School (CR – FFS) and Farmer Business School. This improvement in the integrated curriculum can change individual and community perspectives, improve farm practices, reduce the impacts of climate-related hazards and risks, provide sustainable livelihoods and enhance farmers’ participation in agri-enterprises. The CR-CBFS season-long training exercises will integrate climate risks and forecasts in farmers’ decision-making, provide technical and business lenses for improved farm productivity and profitability through the integration of complementary enterprises such as intercropping, livestock, value-adding and processing that consider environmental, socio-cultural and economic factors.

Stuck in the Wild—The Hydrology of the Teklanika River (Alaska) in the Summer of 1992

In late spring of 1992, Christopher McCandless crossed the Teklanika River, west of Healy, Alaska (United States). His summer has been well documented both in the book and the movie ‘Into the Wild.’ In early summer of 1992, he attempted to cross back over the river, but was stopped by high waters and he died later that summer. This paper investigates the hydrologic conditions of the Teklanika River watershed. We consider both climatological conditions and also conditions during the summer of 1992. We run process-based snowpack and runoff models in order to estimate the river hydrograph at the point of Mr. McCandless’ attempted crossing. Our results demonstrate that the Teklanika river is very flashy during the summer, responding rapidly to strong episodic rainfall events. The main snowmelt signal occurred in mid-to-late May, after Mr. McCandless’ first crossing and before his second attempt. The specific day of his attempted re-crossing corresponded to a large runoff event, driven by rainfall. We conclude that Mr. McCandless had unfortunate timing and that, had he tried to cross a day or two earlier or later, the outcome may have been different. This paper is also an opportunity to explore the hydrologic compromises that must be made when trying to study ungauged, or poorly gauged, areas. There is a spectrum of choices regarding input datasets and methodological simplifications and the correct location on that spectrum will depend on the particular watershed the objectives and expectations of the study.

Long-term hillslope erosion and landslide–channel coupling in the area of the catastrophic Wenchuan earthquake

Approximately 200,000 landslides were triggered by the 2008 Wenchuan earthquake and subsequent strong rainfall events, and the amount of landslide sediment delivered to the channels within catchments depended on the amount of landslide debris generated by the earthquake and the amount of post-earthquake rainfall. To better understand long-term hillslope erosion and the long-term changes in landslide–channel coupling, this study quantifies the coupling degree of landslide–channel by defining a landslide-channel coupling index (LCCI) and estimates the long-term hillslope erosion driven by landslides within 12 debris flow basins. We track landslide activity using multiyear imagery from 2008 to 2019, and the landslide ratio, landslide new regeneration ratio, and landslide reactivated ratio indicate that the overall landslide activity decayed following the Wenchuan earthquake. The calculation results of the coupling index illustrate that the coupling degree of landslide–channel in the study area follows a power law trend of decay over time. However, due to the influence of landslide activity, the coupling index decreased significantly in the first 5 years after the Wenchuan earthquake and then decreased slowly. The hillslope erosion driven by landslides is estimated using a conservative statistical model. The result shows that the landslide-driven hillslope erosion has decayed following a power law, and elevated levels of erosion may last for an unexpectedly long period. In addition, the landslide–channel coupling degree affects the movement of landslide sediment to channels. While the coupling degree of landslide–channel and the amount of landslide sediment supplied to the channels have decreased significantly in recent years, abundant landslide sediment could still be delivered to the channels when strong rainfall occurs in this region. Furthermore, a considerable amount of sediment appears to remain within the tributary channels and trunk channels, which means the activity of debris flow may last longer period than hillslope erosion.

Effects of tillage-induced soil surface roughness on the generation of surface–subsurface flow and soil loss in the red soil sloping farmland of southern China

The role of tillage-induced soil surface roughness (SSR) in altering surface–subsurface flow and soil loss needs to be investigated in the red soil region of southern China. In this study, two different roughness conditions (smooth surface and rough surface), produced by plowing with and without flattening, were employed to assess the effects of surface roughness on rainfall redistribution, surface and subsurface flow generation, and soil loss. In-situ rainfall simulations with three different rainfall intensities (30, 60, and 90 mm h−1) during 180 min of rainfall were tested for a steep farmland sloped at 15°. The results showed that the rough surface had a higher capability for improving subsurface flow, whereby 34% of the rainfall changed into surface flow, and 24% changed into subsurface flow; whereas the proportions of surface and subsurface flow on the smooth surface were 40% and 16%, respectively. The rough surface exhibited a faster initial generation of surface flow and subsurface flow, and the progress of erosion from sheet erosion to rill erosion was more rapid than on the smooth surface, leading to a higher sediment yield from the rough surface under stronger rainfall events. However, the rough surface demonstrated enhanced infiltration behavior and prevention of soil loss under low-intensity rainfall events. The difference in soil crusts on smooth and rough surfaces was the dominant factor affecting surface–subsurface flow generation and soil loss from the red soil sloping farmland. The roughness decreased on the rough surface and increased on the smooth surface during rainfall events. The interactions between surface and subsurface flow should be considered to evaluate soil loss; hence, this research provides a comprehensive understanding of the impact of tillage activities on soil erosion.

Morphometry and Debris-Flow Susceptibility Map in Mountain Drainage Basins of the Vallo di Diano, Southern Italy

In watershed mountain basins, affected in the last decades by strong rainfall events, the role of debris-flow and debris flood processes was investigated. Morphometric parameters have proven to be useful first-approximation indicators in discriminating those processes, especially in large areas of investigation. Computation of morphometric parameters in 19 watershed mountain basins of the western side valley of the Vallo di Diano intermontane basin (southern Italy) was carried out. This procedure was integrated by a semi-automatic elaboration of the potential susceptibility to debris flows, using Flow-R modelling. This software, providing an empirical model of the preliminary susceptibility assessment at a regional scale, was applied in many countries of the world. The implementation of Flow-R modelling requires a GIS application and some thematic base maps extracted using DEMs analysis. A 5-meter-resolution DEM has been used in order to produce the susceptibility maps of the whole study area, and the results are compared and discussed with the real debris flow/flood events that occurred in 1993, 2005, 2010, and 2017 in the studied area. The results have provided a good reliability of Flow-R modelling within small catchment mountain basins.

High Rainfall Inhibited Soil Respiration in an Asian Monsoon Forest in Taiwan

Soil respiration represents the second largest carbon flux, next to photosynthesis of the terrestrial biosphere, and thus plays a dual role in regional and global carbon cycles. However, soil respiration in Asian monsoon forests with high rainfall has rarely been studied. In this study, we continuously measured soil respiration using a 12-channel automated chamber system in a 61-year-old Japanese cedar forest in central Taiwan with annual rainfall greater than 2500 mm. A 4-year (2011–2014) continuous half-hourly dataset was used to quantify the influences of soil temperature and moisture, especially rainfall events, on both total soil respiration (Rs) and heterotrophic respiration (Rh). The annual mean Rs was approximately 10.8 t C ha−1 (ranging from 10.7 to 10.9) t C ha−1, with Rh contributing approximately 74.6% (ranging from 71.7% to 80.2%). Large seasonal variations in both Rs and Rh were primarily controlled by soil temperature. Over 45.8% of total annual rainfall amounts were provided by strong rainfall events (over 50 mm), and over 40% of rainfall events occurred during summers between 2012 and 2014. These strong rainfall events caused rainwater to enter soil pores and cover the soil surface, which resulted in limited soil microorganism activity and, consequently, restricted CO2 production. The mean Q10 values were 2.38 (ranging from 1.77 to 2.65) and 2.02 (ranging from 1.71 to 2.34) for Rs and Rh, respectively. The Q10 values in this study, which were lower than in global forest ecosystems, may imply that the interannual Rs values observed in this study that were caused by high rainfall were less temperature-dependent than the Rs levels in global forest ecosystems. Both Rs and Rh were negatively correlated with soil moisture, which indicated that the soil moisture levels in the studied forest were usually under saturated conditions. These results also provide the lack of data for respiration in the Asian monsoon region under high-rainfall conditions.

Synoptic-to-Regional-Scale Analysis of Rainfall in the Atacama Desert (18°–26°S) Using a Long-Term Simulation with WRF

AbstractIn this study, reanalysis data and a long-term simulation with the regional climate model WRF (1982–2017; 10 km resolution) is used to analyze synoptic and regional processes associated with rainfall events in the Atacama Desert. Five composites, each with 10 WRF-simulated rainfall events, are studied. They are selected based on a clustering and comprise the top winter events in South Atacama (23°–26°S), Southeast Atacama, and North Atacama (18°–23°S), and the top summer events in North Atacama and Northeast Atacama. Winter rainfall events in South Atacama are mostly associated with strong low pressure systems over the southeast Pacific and atmospheric rivers at their foreside, while cutoff lows occurring anomalously far north facilitate strong rainfall in North Atacama. Accordingly, tropical continental areas and the remote tropical and subtropical Pacific are identified as primary moisture sources, and moisture transport toward the Atacama Desert mainly takes place in the free troposphere (above 800 hPa). Strong summer rainfall events in North Atacama and Northeast Atacama are associated with a southward displaced Bolivian high. During rainfall events in North Atacama the high is shifted westward when compared to the Northeast Atacama events. Consequently, northern Chile is located at the northern periphery of the Bolivian high and the resulting strong easterlies may push strong convective systems from the Altiplano, toward the Atacama coast. Detailed analyses of individual rainfall events reveal that the most important synoptic patterns associated with rainfall not only control the synoptic-scale moisture transport into the Atacama Desert, but also decisively influence the regional atmospheric circulation.

Comparison of Heavy Rainfall Events Originated from Different Directions of Beijing City

Strong rainfall events originated from the northeast (NE) and southwest (SW) directions of the plain area of Beijing City (BJP) over 8 recent warm seasons (May-September of 2009–2016) were analyzed by using hourly merged rainfall, satellite brightness temperature, and the fifth-generation ECMWF reanalysis (ERA5) data. Such heavy regional rainfall events (RREs) with different origins present quite different features in both the precipitation itself and its corresponding circulations. The heavy RREs originated from the SW occur more frequently in the flood season of North China (July and August), and the peak time of rainfall occurrences is in the early morning. They are linked with stronger large-scale circulation forcing, compared with the NE-originated events. Meanwhile, the ratio of heavy rainfall to the total rainfall in SW-originated events, the mean spatial coverage of rainfall, and associated convective index, are also larger, for the SW events. The heavy RREs from the NE occur more frequently in June and July (before the traditional flood season), with a more apparent afternoon peak. They exhibit stronger convective features, with higher maximum convective index values, but the large-scale forcing is weaker at the hour of onset. These features of the RREs from different directions of Beijing City and associated precursor circulation signals help better forecast RREs over the BJP.

Hygienic Condition of Different Water Sources in the Kharaa River Basin, Mongolia in the Light of a Rapid Warming Trend

Mongolia is a water-scarce land-locked country, and available water resources are utilized for multiple purposes including irrigation, food preparation, drinking water for livestock and people. Limited data availability on water hygiene means that the related risks to public health are only partially understood. This is particularly problematic due to the widespread use of unimproved water sources such as surface water and water from simple shallow wells. Based on two field surveys in the Kharaa River Basin in spring 2017 and 2018, we assessed the presence and quantity of total coliforms (TC), fecal coliforms (FC), and E. coli bacteria in surface waters and wells and investigated potential linkages between temperature and hygiene. In the Kharaa River and its tributaries, TC concentrations averaged at a most probable number of (MPN) of 754 ± 761 per 100 mL and FC concentrations at an MPN of 31 ± 33. Only small and non-significant correlations between coliform concentrations and temperature were identified. Coliforms concentrations in wells were lower (average MPN for TC: 550 ± 1286, and for FC 58 ± 253). There was considerable variation between wells, with moderate but significant correlations between temperature and bacterial counts. Low water temperatures in April and May (just above freezing to less than 6.5 °C in wells and 7.5 °C to 14.5 °C in the river system) and the positive correlations between temperature and coliform concentrations particularly for well samples indicate that further warming is likely to increase the risks of microbiological water pollution. In the future, this should be complemented by modeling at a watershed scale. This should include the consideration of a trend towards stronger rainfall events, changes in livestock density, and urban sewage treatment and discharge, which are other likely drivers of changes in water hygiene.

Relationship of sediment influx to ostracode populations on the variably deforested Luiche and Mahale platform coasts of Lake Tanganyika, Tanzania

We investigated the hypothesis that ostracode populations are sensitive to variations in sediment discharge related to watershed differences at Lake Tanganyika. Many ostracode species are documented to be sensitive to high turbidity which increases during runoff from strong rainfall events and changes in ostracode populations can impact organisms higher in the food web. We compared surficial death assemblages of ostracodes around two sites with extensive shell beds, the highly deforested Luiche Platform area, heavily populated since the 20th Century, and the less deforested Mahale Platform area, with recent population increases, to understand the impacts of increasing sedimentation within and between sites. The study found that whereas the Mahale Platform area is less disturbed, the faunal differences between sites is not large. The data showed high species richness and abundance of ostracodes at 10–20 m depth at both sites, within shell bed zones, with no statistical difference in raw species richness between the sites. The Mahale Mountain area ostracode populations were however statistically more diverse (Shannon H) than at Luiche. We conducted a multi-response permutation procedure and found that the sites are statistically different, but with very small differences in species richness and ostracode abundance. Non-metric multidimensional scaling ordination of species assemblages shows that most samples overlap on both major axes. This study synthesized with ongoing research about shell bed communities in less disturbed regions of the lake will give insights into how conservation projects can be optimized to preserve the lake’s benthic ecosystem from the effects of deforestation.

Early and mid-Holocene hydroclimate change recorded in tufa deposits in the Jiuzhaigou gully, eastern Tibetan Plateau

Rhythmic nature of tufa deposits and analysis of hydrochemical proxies offer the potential to reconstruct the history of regional palaeo-hydrological and palaeo-climatic change. This paper investigates the tufa deposits of Sparkling Lake in the Jiuzhaigou gully of the eastern Tibetan Plateau (ETP). Detailed analysis of mineral composition, major elements and stable isotope (δ13C, δ18O) distinguished seven “dirty tufa layers” that are characterized by quartz-rich sediments, high kaolinite and high K, Na and Al. Compared with clean tufa deposits, dirty components in the tufa deposits were a result of surface soil erosion activity during strong monsoon rainfall periods within the catchment. The chronology of tufa deposits is established by using radiocarbon (14C) dating of organic material from the dirty tufa layers. Seven flood-rich periods and eight flood-poor periods during the early and mid-Holocene were recorded by the dirty tufa layers interbedded with clean tufa layers in the Jiuzhaigou gully. The tufa records are more sensitive response to regional hydroclimate change, in comparison with the peat, lake sediments and stalagmite records. The low values of δ18O and δ13C in the dirty tufa layers indicate the flood-rich periods (10310–8390, 7120, 6910, 6340, 5900, 5620, 5020 a BP) were mainly triggered by strong monsoon rainfall events during early and mid-Holocene. Considering the chronological uncertainties and sampling resolution, some other abrupt climate events (i.e, 8200 a BP and 5500 a BP) may be also recorded in the tufa deposits. These results greatly improve our understanding of hydroclimate change in the ETP during the early and mid-Holocene.

Nutrient loss is sensitive to land cover changes and slope gradients of agricultural hillsides: Evidence from four contrasting pond systems in a hilly catchment

Intensive agricultural cultivation in hilly catchments is subject to significant environmental risks, because the local terrain and exceptionally fragile ecosystem usually promote high levels of nutrient loss. In order to assess such negative effects, we compared long-term (2012–2018) water quality dynamics of four ponds that are fed by runoff from agricultural hillsides with contrasting slopes and land cover near Tianmu Lake in Eastern China. Averaged total nitrogen (TN) levels in ponds increased from 7.0 mg L−1 to 10.0 mg L−1 when the cultivated slopes above them doubled from 8° to 16°. In contrast, total phosphorus (TP) levels varied modestly from 0.05 to 0.07 mg L−1 among the four ponds. Values were lower when drained hillslopes had good vegetation coverage and/or buffer strips. Redundancy analysis (RDA) indicated that relatively high precipitation is the determining factor for N loss from gentle hillsides, but as slope gradients increase, the frequency of rainfall events becomes the major influential factor. TP loss was associated with strong rainfall events and can be greatly reduced if hillsides are well covered with vegetation. When vegetation cover is removed, nutrient loss, especially N, is heightened. Our results underscore the significance of agricultural cultivation of steep hillsides in exacerbating N and P pollution and highlight the value of forests and grasslands in reducing nutrient loss from these sensitive areas. An integrated strategy that includes controlling land exploitation, source control, delivery interception, and pond management should be considered to minimize nutrient loss in hilly areas prone to rapid agricultural expansion.

A model study of terraced riverbeds as novel ecosystems

Riverbed terracing has been introduced in ancient times to retain water and soil, to reduce hydrological connectivity and erosion and to increase primary and secondary productivity of agro-ecological systems. These presently abandoned human-made landscapes have become novel ecosystems and a potential source of ecosystem services to humans in drylands. We use a mathematical-modeling approach to study factors that regulate terraced riverbeds and affect community and ecosystem attributes such as productivity, functional diversity and resilience to droughts. We introduce a model that captures the relationships between rainfall pattern, runoff coupling between adjacent terraces, and vegetation growth, taking into account competition for water and light. We found that a large number of weak rainfall events results in lower total biomass and functional diversity across the terraced riverbed compared with a few strong rainfall events. We further analyzed the filtering of species traits from pools of functional groups that make different tradeoffs between investment in above-ground biomass to capture canopy resources and investment in below-ground biomass to capture soil resources. Pools characterized by concave tradeoffs give rise to higher functional diversity, lower biomass production and lower resilience to droughts, as compared with convex pools. New empirical studies are needed to test these model predictions.