Large Rainfall Research Articles

Future changes in the Dominant Source Layer of riparian lateral water fluxes in a subhumid Mediterranean catchment

The ‘Dominant Source Layer’ (DSL) is defined as the riparian zone (RZ) depth stratum that contributes the most to water and solute fluxes to streams. The concept can be used to explain timing and amount of matter transferred from RZs to streams in forest headwaters. Here, we investigated the potential impact of future climate changes on the long-term position of the DSL in a subhumid Mediterranean headwater catchment. We used the rainfall-runoff model PERSiST to simulate reference (1981–2000) and future (2081–2100) stream runoff. The latter were simulated using synthetic temperature, precipitation, and inter-event length scenarios in order to simulate possible effects of changes in temperature, rainfall amount, and rainfall event frequency and intensity. Simulated stream runoff was then used to estimate RZ groundwater tables and the proportion of lateral water flux at every depth in the riparian profile; and hence the DSL. Our simulations indicated that future changes in temperature and precipitation will have a similar impact on the long-term DSL position. Nearly all scenarios projected that, together with reductions in stream runoff and water exports, the DSL will move down in the future, by as much as ca. 30 cm. Shallow organic-rich layers in the RZ will only be hydrologically activated during sporadic, large rainfall episodes predicted for the most extreme inter-event length scenarios. Consequently, terrestrial organic matter inputs to streams will decrease, likely reducing catchment organic matter exports and stream dissolved organic carbon concentrations. This study highlights the importance of identifying vertical, hydrologically active layers in the RZ for a better understanding of the potential impact of future climate on lateral water transfer and their relationship with surface water quality and carbon cycling.

Soil Moisture Dynamics in Response to Precipitation and Thinning in a Semi-Dry Forest in Northern Mexico

Understanding soil moisture behavior in semi-dry forests is essential for evaluating the impact of forest management on water availability. The objective of the study was to analyze soil moisture based in storm observations in three micro-catchments (0.19, 0.20, and 0.27 ha) with similar tree densities, and subject to different thinning intensities in a semi-dry forest in Chihuahua, Mexico. Vegetation, soil characteristics, precipitation, and volumetric water content were measured before thinning (2018), and after 0%, 40%, and 80% thinning for each micro-catchment (2019). Soil moisture was low and relatively similar among the three micro-catchments in 2018 (mean = 8.5%), and only large rainfall events (>30 mm) increased soil moisture significantly (29–52%). After thinning, soil moisture was higher and significantly different among the micro-catchments only during small rainfall events (<10 mm), while a difference was not noted during large events. The difference before–after during small rainfall events was not significant for the control (0% thinning); whereas 40% and 80% thinning increased soil moisture significantly by 40% and 53%, respectively. Knowledge of the response of soil moisture as a result of thinning and rainfall characteristics has important implications, especially for evaluating the impact of forest management on water availability.

Effects of slope length on soil erosion of Karst slope under different rainfall conditions

Based on the runoff and sediment yield data from 59 erosive rainfall plots with different slope lengths (5, 10, 15, 20, 25 m) in Shiqiao small watershed of Guizhou Province from 2012 to 2014, we analyzed the relationship between runoff and sediment yield and slope length under diffe-rent rainfall conditions. The results showed that, with the increases of slope length, the runoff yield of slope showed a 'V-shape' pattern, the sediment yield of slope increased first and then decreased. According to rainfall amount, rainfall duration, and average rainfall intensity, the 59 erosive rainfall in the study area could be divided into three types, including type A with short duration, heavy rain intensity and small rainfall, type B with medium duration, light rain intensity and medium rainfall, and type C with long duration, medium rain intensity and large rainfall. The relationships between runoff and sediment yield and slope length were different under different rainfall patterns. There was about 20 m critical slope length of sediment yield under type A and B. The sediment yield gradually increased with the increases of slope length under type C. There was a good cubic function relationship between slope length and runoff and sediment yield under different rainfall patterns. The variable amplitude of runoff and sediment yield was different among different slope lengths. Except the slope length of 15-20 m, the variable amplitude of runoff and sediment yield under type C was relatively large. The variation amplitude of sediment yield was significantly higher than that under other rainfall patterns. The total runoff yield under different rainfall patterns was type A>B>C. The sediment yield under type B was the smallest, that of type A at the slope length of 20 m was the largest and that of type C at other slope lengths was the largest. The correlation between compound rainfall factors and runoff and sediment yield was better than that of single rainfall factor under type A (common rainfall type in the study area). Rainfall amount (P), the pro-duct of rainfall duration and maximum 30 min rainfall intensity (TI30), product of rainfall duration and average rainfall intensity (TI), product of rainfall amount and rainfall duration (PT) were significantly correlated with the runoff and sediment yield. Among those factors, P and TI had the strongest correlation with runoff. Further, the relationship between them and runoff under different slope lengths could be expressed by linear equation and S-curve. There was a good cubic function relationship between the sediment yield and its corresponding rainfall factors under different slope lengths.

Nitrous Oxide and Methane Emissions from Beef Cattle Feedyard Pens Following Large Rainfall Events

HighlightsNitrous oxide and methane emissions were measured from a commercial beef feedyard following large rainfall events.Nitrous oxide emissions dropped below detection levels for ten days following a 77 mm rainfall event.Daily N2O and CH4 emissions followed a diel pattern, peaking at manure temperatures of 36°C to 38°C.Results will be used to refine empirical models for predicting GHG emissions from open-lot feedyards.Abstract. More than six million beef cattle are fed annually in feedyards on the semiarid Southern Great Plains (SGP). Manure deposited on the open-lot pen surfaces contributes to greenhouse gas (GHG) emissions. Nitrous oxide (N2O) and methane (CH4) are GHGs linked to climate change, and both have global warming potentials greater than carbon dioxide (CO2). Two sampling campaigns were conducted in 2019 to quantify N2O and CH4 emissions from open-lot pen surfaces. The occurrence of large, unforecast rainfall events during both campaigns provided an opportunity to compare GHG emissions from the dry manure before rainfall and from the wetted pen surface for one to two weeks following precipitation. Temporal variability was quantified by continuous sampling using six to eight automated flux chambers, a multiplexer system, and real-time analyzers. Spatial variability was quantified using a recirculating portable chamber on a 5 × 8 grid. Nitrous oxide emissions dropped below detection levels for ten days after the precipitation event. Nitrous oxide emissions were related to nitrification or other aerobic processes. Methane emissions dropped below detection levels for five days after the precipitation event and then increased to pre-rainfall levels by day 8. When present, N2O and CH4 emissions followed a diel pattern, with the highest emissions occurring during the afternoon when manure pack temperatures at the 25 mm depth were 36°C to 38°C and ambient temperatures were 31°C to 32°C. Average CH4 emissions from the feedyard pen surface were 96-fold lower than estimated enteric CH4 emissions. The results of this field research will be used to refine empirical models for predicting annual N2O and CH4 emissions from open-lot beef cattle feedyards on the semiarid SGP. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Nitrous oxide, Rainfall.

Water footprint of milk production systems in semi-arid plains of North Africa

Water resources are becoming scarce and must be preserved. The significant use of water is linked to agriculture in general and to livestock in particular. Very little research in semi-arid regions has been devoted to assessing the contribution of ruminants to water scarcity. This contribution explores the relationships between dairy farming and the various water resources available in an ecosystem with climatic constraints. To meet future food demand while sustainably managing the available land and water resources, dairy farm systems in semi-arid regions must adapt in response to climate and socio-economic change. In this study, we focus on the south Mediterranean region to analyze the key factors influencing water productivity in dairy farming, especially in context characterized by water scarcity. In order to characterize the relationship between dairy cattle breeding and water resources, a monitoring of 40 dairy cattle stables has been carried out in a semi-arid region. The technical and economic parameters of each farm were evaluated: the use of water according to their origins to the production of fodder by source, the contribution of virtual water off the farm, the total fodder biomass, feeding system practiced on the farms and the performances achieved. Analysis of the data indicates that productivity of fodder in dry matter differ between the two systems with values of the order of 12520 to 17188 kg/ha (p<0.05) respectively for type extensive and intensive systems. The milk yield per cow did not exceed an average value of 3680 kg (rang 3240 to 4120 kg. The mean gross margin per kilogram of milk was low, not exceeding 0.13?. A significant effect (p<0.05) of the value of the water footprint between the two dairy farm systems with an average of around 2.05m3/kg of milk (range 1.96 to 2.15 respectively for intensive and extensive farms). The contribution of rainfall is estimated at 57% and the rest is represented by the participation of irrigation and virtual water with 18% and 25% respectively. Necessary actions must be taken along the milk production process in order to improve the productivity of water for forage production and the milk which depends in large part on annual rainfall and to a lesser extent on groundwater.

Backward trajectory analysis of southern California atmospheric rivers

Atmospheric rivers (ARs) are filamentary channels of high water vapor flux that transfer moisture horizontally through the atmosphere at low levels. ARs are often responsible for large annual rainfall totals as well as high-intensity storms due to orographic forcing. ARs are important features when predicting hazardous events such as flooding and are vital components of many regional water budgets. This is especially true for drought-prone areas such as southern California (SCA), which experiences relatively few storms per season, many from AR events. Here, we use a Lagrangian model to create backward air parcel trajectories of 159 AR events that made landfall on the US west coast from December 2004 to December 2015. Trajectories are used to examine the lifecycles and movements of these ARs and to differentiate ARs that made landfall in different regions. Prior to landfall, SCA ARs share similarities to but also have distinct differences from other ARs. At 1000 m above mean sea level (MSL), SCA AR trajectories travel shorter distances over the same 72 h time frame than trajectories for ARs that made landfall farther north. Additionally, along-trajectory measurements for SCA ARs tend to be warmer and have higher specific humidity values. This applies to both the 1000 and 2000 m MSL levels. These results imply that SCA ARs move slower and have the potential to produce higher intensity storms at landfall. An analysis of a case study event of an extreme AR that made landfall in SCA on 17 February 2017 confirms these results.

Evaluating the effects of timber harvest on hydrologically sensitive areas and hydrologic response

Effects of forest treatments on watershed hydrology in terms of water yield and runoff processes is a primary concern. This paper evaluates the effects of long-term land cover change on hydrological processes in the Mica Creek Experimental Watershed (MCEW) in northern Idaho, USA. In the MCEW, effects of clearcut and partial cut harvest practices on streamflow were monitored and evaluated from 1991 to 2013. Firstly, snowpack dynamics in terms of snowmelt timing and average melt rate under different elevations, aspects, land covers, and climate conditions were analyzed at the point-scale with the snow accumulation and melt (SAM) model from the perspective of the energy balance. Then, the grid-based soil moisture routing (SMR) hydrology model was used to provide temporal and spatial hydrological changes in the MCEW. We assigned locations as hydrologically sensitive areas (HSAs) based on the probability of runoff generation (P(Ai = HS)) to capture potential downstream environmental effects of actual land cover change and optimal harvest patterns. The results highlight the strong impacts timber harvest can have on increasing streamflow and, in particular, peak flow. On average, the daily averaged degree of saturation increased by 20% after timber harvest resulting in higher risks of flooding from large rainfall events. Three logging scenarios including logging in areas with low P(Ai = HS), high P(Ai = HS), and in the entire watershed area, showed that logging areas had a positive relationship with water yield and that more extreme peak flow was likely to occur after clearcutting in high P(Ai = HS) areas (high elevation) under rainfall driven events or logging in low P(Ai = HS) areas (medium elevation) during snowmelt dominated events. Clearcutting on south-facing slopes at medium elevation strongly increased the average melt rate leading to potential flooding if a snowpack was present and temperatures increased. Scenario analysis suggests that partial cutting in areas with low P(Ai = HS) would reduce peak flow amount by as much as 40%. However, for watersheds to be logged entirely, choosing proper harvest locations such as clearcutting in high P(Ai = HS) areas having large snow events may effectively reduce extreme peak flow from spring snowmelt. Our findings inform forest management decisions favoring partial cutting over clearcutting, and how to avoid concentrating harvest practices in HSAs by adapting spatial distribution and timing of harvesting to climate conditions to minimize impacts on the water cycle.

Future Crop Yield Projections Using a Multi-model Set of Regional Climate Models and a Plausible Adaptation Practice in the Southeast United States

Since maize, peanut, and cotton are economically valuable crops in the southeast United States, their yield amount changes in a future climate are attention-grabbing statistics demanded by associated stakeholders and policymakers. The Crop System Modeling—Decision Support System for Agrotechnology Transfer (CSM-DSSAT) models of maize, peanut, and cotton are, respectively, driven by the North American Regional Climate Change Assessment Program (NARCCAP) Phase II regional climate models to estimate current (1971–2000) and future (2041–2070) crop yield amounts. In particular, the future weather/climate data are based on the Special Report on Emission Scenarios (SRES) A2 emissions scenario. The NARCCAP realizations show on average that there will be large temperature increases (~2.7 °C) and minor rainfall decreases (~−0.10 mm/day) with pattern shifts in the southeast United States. With these future climate projections, the overall future crop yield amounts appear to be reduced under rainfed conditions. A better estimate of future crop yield amounts might be achievable by utilizing the so-called weighted ensemble method. It is proposed that the reduced crop yield amounts in the future could be mitigated by altering the currently adopted local planting dates without any irrigation support.

Monitoring the Hydrological Balance of a Landslide-Prone Slope Covered by Pyroclastic Deposits over Limestone Fractured Bedrock

Many mountainous areas in Campania, Southern Italy, are characterized by steep slopes covered by loose unsaturated pyroclastic deposits laying upon fractured limestone bedrock. The soil covers are mainly constituted by layers of ashes and pumices. Large and intense rainfall events trigger shallow landslides, often turning into debris flows that cause huge damage and casualties. The slope of Cervinara, around 40 km Northeast of Naples, was involved in a catastrophic flowslide on 16 December 1999, triggered by a rainstorm of 325 mm in 48 h. To capture the main effects of precipitation on the slope stability, hydro-meteorological monitoring activities have been carried out at the slope to assess the water balance for three years (2017–2020). The field monitoring data allowed the identification of the complex hydrological processes involving the unsaturated pyroclastic soil and the shallow groundwater system developing in the limestone bedrock, which control the conditions that potentially predispose the slope to landslide triggering. Specifically, late autumn has been identified as the potentially most critical period, when slope drainage processes are not yet effective, and soil covers already receive large amounts of precipitation.

Leaf litter of two riparian tree species has contrasting effects on nutrients leaching from soil during large rainfall events

One goal of revegetating riparian zones is to mitigate nutrient movement into waterways, however release of dissolved nutrients and organic compounds from decaying leaf litter during rainfall may partially offset these benefits. We aim to understand how litter-derived nutrients and organics affect nutrient leaching from riparian soil, and how tree species affect these processes. In the laboratory we simulated large rainfall events through the leaf litter of two riparian woody tree species, Eucalyptus tereticornis and Casuarina cunninghamiana, with and without subsequent leaching through soil, as well as soil alone. We compared the forms and loads of nitrogen and phosphorus in leachate. Litter of both tree species stimulated additional nitrate release from soil (~100–200%) compared to bare soil. More ammonium and dissolved organic nitrogen also leached from soil with E. tereticornis litter, whereas less leached with C. cunninghamiana litter. More phosphate leached from soil with either species litter compared to bare soil. Increased nitrogen releases from soil with litter were greater than inputs from litter, suggesting they are driven by positive priming of soil microbial processes, whereas litter inputs increased phosphorus leaching. This information could be combined with rates of other riparian nutrient processes (e.g. plant uptake and denitrification) to quantify the net impact of trees on nutrient retention in riparian zones.

Assessing the significance of wet‐canopy evaporation from forests during extreme rainfall events for flood mitigation in mountainous regions of theUnited Kingdom

AbstractThere is increased interest in the potential of tree planting to help mitigate flooding usingnature‐based solutionsornatural flood management. However, many publications based upon catchment studies conclude that, as flood magnitude increases, benefit from forest cover declines and is insignificant for extreme flood events. These conclusions conflict with estimates of evaporation loss from forest plot observations of gross rainfall, through fall and stem flow. This study explores data from existing studies to assess the magnitudes of evaporation and attempts to identify the meteorological conditions under which they would be supported. This is achieved using rainfall event data collated from publications and data archives from studies undertaken in temperate environments around the world. The meteorological conditions required to drive the observed evaporation losses are explored theoretically using the Penman–Monteith equation. The results of this theoretical analysis are compared with the prevailing meteorological conditions during large and extreme rainfall events in mountainous regions of the United Kingdom to assess the likely significance of wet canopy evaporation loss. The collated dataset showed that eventEwclosses between approximately 2 and 38% of gross rainfall (1.5 to 39.4 mm day−1) have been observed during large rainfall events (up to 118 mm day−1) and that there are few data for extreme events (>150 mm day−1). Event data greater than 150 mm (reported separately) included similarly high percentage evaporation losses. Theoretical estimates of wet‐canopy evaporation indicated that, to reproduce the losses towards the high end of these observations, relative humidity and the aerodynamic resistance for vapour transport needed to be lower than approximately 97.5% and 0.5 to 2 s m−1respectively. Surface meteorological data during large and extreme rainfall events in the United Kingdom suggest that conditions favourable for high wet‐canopy evaporation are not uncommon and indicate that significant evaporation losses during large and extreme events are possible but not for all events and not at all locations. Thus the disparity with the results from catchment studies remains.

Rainfall affected stability analysis of Maddingley Brown Coal eastern batter using Plaxis 3D

Rainfall is a common factor that triggers the instability of Victorian Brown Coal (VBC) open pits which facilitate some of the largest brown coal mining operations. There has been no relevant study on rainfall-induced slope instability of VBC open pits in literature. In this paper, a three-dimensional (3D) two-phase (fluid-solid) coupled finite element method (FEM) was employed to investigate the stability of Maddingley Brown Coal (MBC) eastern batter under different rainfall conditions. It was found that the batter tends to lead a circular failure path during large rainfall. With the increase in either precipitation period or rainfall intensity, the deformation, excess pore pressure and active pressure increased, while the matric suction decreased. The hydrostatic force in the confined aquifer underlying the brown coal seam increased during rainfall; meanwhile, the resisting force decreased. As a result, the shear strength decreased and thereby the stability of the batter decreased. The safety factor and the critical failure path of the eastern batter simulated in this study were consistent with the previous study on the Northern batter. This study is a strong supplement to the literature on rainfall-induced instability of VBC batters. In the meantime, it is significant to provide a reference to the application of sophisticated 3D numerical modelling for studying slope instability of brown coal and similar mineral deposits.

Evaluation of sedimentation pond performance for a cleaner water production from an open pit mine at the edge of the Alto Tajo Natural Park

Controlling sediment produced by water erosion is the highest environmental challenge in steep, open pit sand mines located in erosive climates. Although restoration is impractical in active mine areas, sedimentation ponds are the Best Available Technique by the European Union to reduce sediment spillages from these environments. Few studies have described and supported such a solution with high resolution data. The María José mine is one of two active kaolin mines in the mining area of the Alto Tajo Natural Park, a highly erosive setting. It has a complex maintained pond system as a hydrologic and sedimentary control measure. In this landscape, mining can only be sustainable if clean water from production is ensured. The pond system retains sediment and water during a rain event, deposits the sediment, and eventually spills the water under controlled events. The María José spillages have been continuously monitored for suspended sediment concentration and water discharge at the mine outlet since 2012. During four years the efficiency of the pond system varied (96.7–99%), producing an average annual sediment yield of 5.6 Mg ha−1 y−1, a reduction of 98.4% compared with the sediment yield reported for similar local mines having no ponds. A quarter of this sediment was produced under controlled spillages allowing runoff management; the rest during large rainfall events when runoff decreased pond efficiency gives rise to an increase in suspended sediment concentration, as is typical of local natural rivers. Provided continuous maintenance, sediment ponds are shown to be a successful method to produce clean water. Successful pond efficiency implies that a mine produces water and sediment during baseflow conditions, allowing sufficient sediment volume to accumulate during rainstorms.

Fırtına Havzasının Bazı Havza Karakteristikleri ile Arazilerin Fizyografik Özelliklere Göre Dağılımlarının Coğrafi Bilgi Sistemleri İle Belirlenmesi

Doğal kaynakların sürdürülebilir planlaması ve yönetimi bütünleşik havza planlama ve yönetimi ilkelerine göre yapılmalıdır. Başarılı bir bütünleşik havza planlamanın ortaya konulabilmesi için planlamanın yapılacağı havzanın alt havzaları ile birlikte sahip olduğu havza karakteristik özellikleri ile arazilerin yükselti, bakı, eğim ve kayaç türlerine göre dağılımlarının doğru bir şekilde belirlenmesi oldukça önemlidir. Bu amaçla çok büyük bir yağış havzası olan Fırtına deresi yağış havzası doğu ve batı olmak üzere iki büyük alt havza gurubuna ayrılmış ve sahip olduğu bazı arazi karakteristikleri ile arazilerin yükselti, eğim, bakı ve kayaç guruplarına göre dağılımları Coğrafi Bilgi Sistemi (CBS) yardımıyla ortaya konulmuştur. Araştırma sonucuna göre Fırtına deresi yağış havzasının drenaj alanı 1155.44 km2’dir. Fırtına deresi batı havza gurubundaki arazilerinin % 60.12’si gölgeli bakılar üzerinde, % 39.88’i güneşli bakılar üzerinde yer almaktadır. Jeolojik formasyonlara göre en geniş arazi varlığı 29041.02 ha (%34.96) ile granit-mikrogranit-granodiorit serisinde ve eğime göre en geniş arazi varlığı 19684.21 ha (%23.70) ile %31-40 eğim gurubunda yer almaktadır. Durak deresi yağış havzası arazilerinin % 53.40’ı gölgeli bakılar, % 46.60’ı güneşli bakılar üzerindedir. Durak havzasında eğime göre en geniş arazi varlığı (8191.90 ha) %31-40 eğim gurubunda ve kayaç gurubuna göre en geniş arazi varlığı %61.68 ile granit-mikrogranit-grandiorit kayaç gurubunda yer almaktadır.

Coupled Climate Model Simulation of Tropical–Extratropical Cloud Bands over Southern Africa

AbstractThere are increasing efforts to use climate model output for adaptation planning, but meanwhile there is often limited understanding of how models represent regional climate. Here we analyze the simulation in global coupled climate models of a key rainfall-generating mechanism over southern Africa: tropical temperate troughs (TTTs). An image-processing algorithm is applied to outgoing longwave radiation data from satellites and models to create TTT event sets. All models investigated produce TTTs with similar circulation features to observed. However, there are large differences among models in the number, intensity, and preferred longitude of events. Five groups of models are identified. The first group generates too few TTTs, and relatively dry conditions over southern Africa compared to other models. A second group generates more TTTs and wet biases. The contrast between these two groups suggests that the number of TTTs could explain intermodel variations in climatological rainfall. However, there is a third group of models that simulate up to 92% more TTTs than observed, but do not have large rainfall biases, as each TTT event is relatively weak. Finally, there are a further two groups that concentrate TTTs over the subcontinent or the ocean, respectively. These distinctions between models are associated with the amount of convective activity in the Congo Basin, the magnitude of moisture fluxes into southern Africa, and the degree of zonal asymmetry in upper-level westerly flow. Model development focused on tropical convection and the representation of orography is needed for improved simulation of TTTs, and therefore southern African rainfall.

Full-Year Evaluation of Nonmeteorological Echo Removal with Dual-Polarization Fuzzy Logic for Two C-Band Radars in a Temperate Climate

AbstractThe Royal Netherlands Meteorological Institute (KNMI) operates two dual-polarization C-band weather radars in simultaneous transmission and reception (STAR; i.e., horizontally and vertically polarized pulses are transmitted simultaneously) mode, providing 2D radar rainfall products. Despite the application of Doppler and speckle filtering, remaining nonmeteorological echoes (especially sea clutter) mainly due to anomalous propagation still pose a problem. This calls for additional filtering algorithms, which can be realized by means of polarimetry. Here we explore the effectiveness of the open-source wradlib fuzzy echo classification and clutter identification based on polarimetric moments. Based on our study, this has recently been extended with the depolarization ratio and clutter phase alignment as new decision variables. Optimal values for weights of the different membership functions and threshold are determined employing a 4-h calibration dataset from one radar. The method is applied to a full year of volumetric data from the two radars in the Dutch temperate climate. The verification focuses on the presence of remaining nonmeteorological echoes by mapping the number of exceedances of radar reflectivity factors for given thresholds. Moreover, accumulated rainfall maps are obtained to detect unrealistically large rainfall depths. The results are compared to those for which no further filtering has been applied. Verification against rain gauge data reveals that only a little precipitation is removed. Because the fuzzy logic algorithm removes many nonmeteorological echoes, the practice to composite data from both radars in logarithmic space to hide these echoes is abandoned and replaced by linearly averaging reflectivities.

The Distribution of Aircraft Icing Accretion in China—Preliminary Study

The icing environment is an important threat to aircraft flight safety. In this work, the icing index is calculated using linear interpolation and based on temperature and relative humidity (RH) curves obtained from radiosonde observations in China. The results show that: (1) there are obvious differences in icing index distribution in parameter over various climatic regions of China. The differences are reflected in duration, main altitude, and ice intensity. The reason for the differences is related to the temperature and humidity environment. (2) Before and after the summer rainfall process, there are obvious changes in the ice accretion index in the 4–6 km altitude area of Northeast China, and the areas with serious ice accretion are coincident with areas with large rainfall estimates. (3) In the process of snowfall in winter, the ground snow has an impact on the ice accumulation index in the east of China. When it is snowing, ice accumulation in low altitudes is serious. The results of this study offer a theoretical basis for prediction and early warning of aircraft icing.

Seasonal variations in the response of soil respiration to rainfall events in a riparian poplar plantation

Rainfall events have profound influence on the soil carbon release in different forest ecosystems. However, seasonal variations in soil respiration (RS) response to rainfall events and associated regulatory processes are not well documented in riparian forest ecosystems to date. We continuously measured soil respiration in a riparian plantation ecosystem from 2015 to 2018 to explore the relationships between soil respiration and rainfall events. Across the 4 years, 83 individual rainfall events were identified for spring, summer and autumn. We found that mean RS rate after rain (post-RS) was significantly higher than that before rain (pre-RS) (p < 0.05) in spring, and the relative change in soil respiration (RSrc) increased against rainfall size due to the stimulation by the significant increases in soil moisture content (ΔSM). In contrast, mean post-RS was lower than pre-RS and RSrc was significantly decreased with the increasing rainfall size (p < 0.01) in summer and autumn. Reduced changes in soil temperature (ΔTS) and increased soil moisture content after rain (post-SM) contributed to the decreased RS due to frequently occurring heavy rain events in summer. Increased ΔSM following rainfall events coupled with groundwater level increase suppressed RSrc in autumn, even though increased ΔTS could offset the negative effects of SM on RS to some extent. In addition, we found that higher post-SM after large rainfall events (>10 mm day−1) changed the response of RS to soil temperature (TS) by reducing the temperature sensitivity (Q10) even in this riparian plantation ecosystem. Our study highlights the importance of integrating seasonal difference in soil respiration response to rainfall events and the impact of large rainfall events on soil C release for estimating forest soil carbon cycling at multiple scales.

Spatial and temporal variability of soil moisture in non-flooded landscape units in Namibian Zambezi region

Climate variability will continue to impact the spatial and temporal variability of soil moisture in different landscapes across the world; and in turn the variability may affect crop production. Non-flood areas in the Namibian Kwalala Landscape of Zambezi (NKLOZ) region are generally relegated to second place, as somewhat marginal for the successful production of major crops such as maize (Zea mays L.). Even when flood water has receded, non-flooded areas which get affected during floods, are still avoided for crop production. This is because residual moisture following the rainy season, is suspected to fall far short of the longer growing duration of maize, to the extent that farmers are too apprehensive to grow maize in such areas. The objective of this study was to determine the effect of seasonal rainfall on spatial and temporal variability of soil moisture within the Namibian Kwalala Landscape of Zambezi (NKLOZ) ecology, and the extent to which soil moisture status and soil temperature patterns (STEPs) characterise soil type (STP) productive potential. Three sensors were setup up at 20, 40 and 60 cm landscape of the NKLOZ, after digging a one-metre trench at each site. Soil moisture and temperature data were retrieved and monitored using Decagon DataTrac 3 software. ANOVA multiple regressions were used to analyse the effects of soil depth, rainfall, and soil temperature on soil moisture. Seasonal rainfall in the NKLOZ during the growing period between October and April (2012-2015) significantly (P &lt; 0.05) and positively affected soil moisture, both in time and space, in recharging soil moisture to sufficiently meet maize crop water requirements in the region. Although it appeared like high amounts of soil moisture sufficiency were as a result of the events of seasonal rainfall received during the growing period, anything received between mid-January and Mid-March was still below the historical minimum and maximum decadal; and in any case late for early planted maize crop. Average soil moisture data indicated for loamy soil (8.30), sandy loam (14.30) and sand at the respective sites suggested a large rainfall season-soil texture interaction. Such an interaction should inform the prudence of production of maize from the point of view of a smart or robust crop system growing planning and management.&#x0D; Key words: Decagon sensors, residual moisture, Zea mays

Prediction of shallow landslides in pyroclastic-covered slopes by coupled modeling of unsaturated and saturated groundwater flow

Slopes covered with unsaturated shallow pyroclastic deposits, lying upon fractured limestone bedrock, are widespread in the mountains around Naples (southern Italy). Rainfall infiltration, reducing soil suction, eventually triggers shallow landslides. While drastic reduction of suction is unanimously recognized as the triggering mechanism, there is still debate about the hydrological processes controlling slope drainage and causing the establishment of landslide predisposing conditions. Field observations at the slope of Cervinara suggested that temporary storage of water in a perched aquifer, in the upper part of the fractured bedrock, may affect the leakage through the soil-bedrock interface. Hence, a physically based model, coupling flows in the unsaturated soil cover and in the perched aquifer, has been applied to three large rainfall events which occurred in December 1999 (when a landslide was triggered), January 2009, and November 2012. The results highlight that the different responses of soil and aquifer to precipitations, related not only to rainfall event characteristics (i.e., duration and mean intensity) but also to the initial conditions of the slope, determined by antecedent precipitations, can play a prominent role in the triggering of landslides. In fact, further simulations with synthetic rainfall events and different initial conditions provide a possible interpretation of the triggering of the landslide of December 1999, indicating that a soil profile with dry conditions at the base and a low level in the perched aquifer, typical of late autumn, can impede the drainage of infiltrating water through the soil-bedrock interface, thus favoring the build-up of pore pressure within the soil cover.