Contribution Of Rainfall Research Articles

Comparing Bayesian and traditional end-member mixing approaches for hydrograph separation in a glacierized basin

Abstract. Tracer data have been successfully used for hydrograph separation in glacierized basins. However, in these basins uncertainties of the hydrograph separation are large and are caused by the spatiotemporal variability in the tracer signatures of water sources, the uncertainty of water sampling, and the mixing model uncertainty. In this study, we used electrical conductivity (EC) measurements and two isotope signatures (δ18O and δ2H) to label the runoff components, including groundwater, snow and glacier meltwater, and rainfall, in a Central Asian glacierized basin. The contributions of runoff components (CRCs) to the total runoff and the corresponding uncertainty were quantified by two mixing approaches, namely a traditional end-member mixing approach (abbreviated as EMMA) and a Bayesian end-member mixing approach. The performance of the two mixing approaches was compared in three seasons that are distinguished as the cold season, snowmelt season, and glacier melt season. The results show the following points. (1) The Bayesian approach generally estimated smaller uncertainty ranges for the CRC when compared to the EMMA. (2) The Bayesian approach tended to be less sensitive to the sampling uncertainties of meltwater than the EMMA. (3) Ignoring the model uncertainty caused by the isotope fractionation likely led to an overestimated rainfall contribution and an underestimated meltwater share in the melt seasons. Our study provides the first comparison of the two end-member mixing approaches for hydrograph separation in glacierized basins and gives insight into the application of tracer-based mixing approaches in similar basins.

Relationship of Weather Types on the Seasonal and Spatial Variability of Rainfall, Runoff, and Sediment Yield in the Western Mediterranean Basin

Rainfall is the key factor to understand soil erosion processes, mechanisms, and rates. Most research was conducted to determine rainfall characteristics and their relationship with soil erosion (erosivity) but there is little information about how atmospheric patterns control soil losses, and this is important to enable sustainable environmental planning and risk prevention. We investigated the temporal and spatial variability of the relationships of rainfall, runoff, and sediment yield with atmospheric patterns (weather types, WTs) in the western Mediterranean basin. For this purpose, we analyzed a large database of rainfall events collected between 1985 and 2015 in 46 experimental plots and catchments with the aim to: (i) evaluate seasonal differences in the contribution of rainfall, runoff, and sediment yield produced by the WTs; and (ii) to analyze the seasonal efficiency of the different WTs (relation frequency and magnitude) related to rainfall, runoff, and sediment yield. The results indicate two different temporal patterns: the first weather type exhibits (during the cold period: autumn and winter) westerly flows that produce the highest rainfall, runoff, and sediment yield values throughout the territory; the second weather type exhibits easterly flows that predominate during the warm period (spring and summer) and it is located on the Mediterranean coast of the Iberian Peninsula. However, the cyclonic situations present high frequency throughout the whole year with a large influence extended around the western Mediterranean basin. Contrary, the anticyclonic situations, despite of its high frequency, do not contribute significantly to the total rainfall, runoff, and sediment (showing the lowest efficiency) because of atmospheric stability that currently characterize this atmospheric pattern. Our approach helps to better understand the relationship of WTs on the seasonal and spatial variability of rainfall, runoff and sediment yield with a regional scale based on the large dataset and number of soil erosion experimental stations.

Comportamento térmico e a contribuição pluvial em Lagoa Seca, Brasil entre 1981-2019

As oscilações térmicas do ar causam efeitos diretos na produção do hortifrutigranjeiro cuja economia é baseada o município de Lagoa Seca. Objetiva-se analisar o comportamento térmico do período de 1981-2019 e suas contribuições pluviais no período chuvoso e seco e as suas variabilidades nas estações dos anos. Utilizou-se das séries mensais e anuais de precipitação e temperatura do ar referente ao período de (1981-2019) procurando-se entender suas flutuações climáticas. As flutuações das temperaturas (máxima, média e mínima) nas estações outono e primavera têm influencias diretas sobres os índices pluviais das mesmas estações. Os eventos de precipitações máximas e mínimas absolutas estão relacionados às flutuações máximas e mínimas das temperaturas estudadas. Estas flutuações das máximas e mínimas absolutas de temperatura e precipitações devem ser estudadas para diferentes regiões do globo, visto que tanto a precipitação como a temperatura local apresentam índices elevados no período chuvoso (março a agosto), seguido do período seco (setembro a abril) que registram temperaturas mais elevadas com alguns momentos de reduções acentuada.

Green Systems Integrated to the Building Envelope: Strategies and Technical Solution for the Italian Case

Green roofs and green and living walls are increasingly seen in cities, because they are an important strategy that addresses some key urban environmental issues and allows the achievement of different benefits. Among these, the most relevant ones are reduction of the “Urban Heat Island” effect, of rainfall contributions to the sewer system, of environmental impact and energy saving, and retention of harmful substance. The study aims to analyze different systems of greenery systems integrated (GSI), green roofs (GR), and green and living walls (GW-LW), as a possible retrofit technique of the envelope of heritage buildings and especially their applications in the context of historic cities in Italy, pointing out positive and negative aspects. Particularly, it pays attention to the green retrofitting of buildings and to the technical problems related to the installation of systems, since at the moment there are already several studies that show the environmental and microclimatic benefits of the integration of vegetation in architecture. This study tries to highlight the series of design procedures necessary both in the preliminary phase and then in the executive phase to relate the GSI to the existing building envelopes. The GR, from the results of the simulations conducted, demonstrate a greater simplicity in their construction, with improvements also from the point of view of the working loads on the existing structures, since the interventions are performed more easily than those on the facade. The study highlights the architectural needs that are not always considered such as the increase in the thickness of the roof and the related need to raise its edges, changing the perspective of the building. On the other hand, the GW and the LW show some complexity in their construction because they must deal with facades often rich in decorative elements and where openings affect the assemblage and connection works such as the tinsmiths of the intrados of the openings. It must be taken into consideration the necessity of having to drill masonry, often inhomogeneous, to connect fixings and the problems of stability this entails must be carefully analyzed.

Tide-rainfall flood quotient: an incisive measure of comprehending a region’s response to storm-tide and pluvial flooding

It is undeniable that coastal regions worldwide are facing unprecedented damages from catastrophic floods attributable to storm-tide (tidal) and extreme rainfall (pluvial). For flood-risk assessment, although recognizing compound impact of these drivers is a conventional practice, the marginal/individual impacts cannot be overlooked. In this letter, we propose a new measure, Tide-Rainfall Flood Quotient (TRFQ), to quantify the driver-specific flood potential of a coastal region arising from storm-tide or rainfall. A set of inundation and hazard maps are derived through a series of numerical and hydrodynamic flood model simulations comprising of design rainfall and design storm-tide. These experiments are demonstrated on three different geographically diverse flood-affected coastal regions in India. The new measure throws light on existing knowledge gaps on the propensity of coastal flooding induced by the marginal/individual contribution of storm-tide and rainfall. It shall prove useful in rationalizing long-term flood management strategies customizable for storm-tide and pluvial dominated global coastal regions.

Combined use of stable isotopes and hydrochemical characteristics to determine streamflow sources in the Jonkershoek catchment, South Africa

ABSTRACT The stable isotopes of water (18O, 2H) and other hydrochemical properties were used to assess seasonal changes between sources of stream water and flow pathways in baseflow conditions for two headwater sub-catchments (∼3 km2) of the Jonkershoek, a mountainous catchment in the Western Cape of South Africa. The sub-catchments differ in land cover, one is dominated by indigenous fynbos vegetation and the other by pine plantation. Stream water, higher elevation springs, and lower elevation groundwater samples were collected monthly from January 2018 to January 2019, and were analysed for stable isotopes, electrical conductivity (EC) and pH. The stream water isotopic values resembled those of groundwater during the dry and wet seasons. Results indicated a steady contribution of spring discharge to streams during the dry season, with rainfall contribution less evident. Wet season flows were attributed to interflow including perennial and ephemeral springs. Spatial variations in EC between the sub-catchments were indicative of a greater proportional input from subsurface water, more evaporation and/or more mineral dissolution in the pine-dominated sub-catchment. The spatiotemporal variability in EC was significantly larger than for the stable isotopes. These findings enabled conceptualization of streamflow generation processes that can support strategic water resource management practices in this region.

Flood-type trend analysis for alpine catchments

ABSTRACT In many places, magnitudes and frequencies of floods are expected to increase due to climate change. To understand these changes better, trend analyses of historical data are helpful. However, traditional trend analyses do not address issues related to shifts in the relative contributions of rainfall versus snowmelt floods, or in the frequency of a particular flood type. We present a novel approach for quantifying such trends in time series of floods using a fuzzy decision tree for event classification and applied it to maximal annual and seasonal floods in 27 alpine catchments for the period 1980–2014. Trends in flood types were studied with Sen’s slope and double mass curves. Our results reveal a decreasing number of rain-on-snow and an increasing number of short rainfall events in all catchments, with flash floods increasing in smaller catchments. Overall, the results demonstrate the value of incorporating a fuzzy flood-type classification into flood trend analyses.

Space–Time Characteristics of Areal Reduction Factors and Rainfall Processes

AbstractWe estimate areal reduction factors (ARFs; the ratio of catchment rainfall and point rainfall) varying in space and time using a fixed-area method for Austria and link them to the dominating rainfall processes in the region. We particularly focus on two subregions in the west and east of the country, where stratiform and convective rainfall processes dominate, respectively. ARFs are estimated using a rainfall dataset of 306 rain gauges with hourly resolution for five durations between 1 h and 1 day. Results indicate that the ARFs decay faster with area in regions of increased convective activity than in regions dominated by stratiform processes. Low ARF values occur where and when lightning activity (as a proxy for convective activity) is high, but some areas with reduced lightning activity exhibit also rather low ARFs as, in summer, convective rainfall can occur in any part of the country. ARFs tend to decrease with increasing return period, possibly because the contribution of convective rainfall is higher. The results of this study are consistent with similar studies in humid climates and provide new insights regarding the relationship of ARFs and dominating rainfall processes.

How Important Is Meltwater to the Chamkhar Chhu Headwaters of the Brahmaputra River?

As our global climate warms, people and economies utilizing water resources sourced by snow and ice melt in mountain areas are disproportionately affected relative to locations that rely on rainfall. Worldwide, the vast majority of those impacted by snowfall changing to rainfall and earlier melt from a warming climate live in Asia. The Brahmaputra River originates in the declining glaciers and snowfields of the Chinese and Bhutanese Himalaya before flowing to the mega population centers of the Bangladesh delta. Bhutan’s economy relies on water resource-dependent hydropower and agriculture imposing important questions about the impact of climate change on the long-term viability of these important economic sectors. To clarify potential effects on water supplies in a warming world, and specifically to quantify the role of meltwater to river discharge in the headwaters of the Brahmaputra basin, we utilize a combined field observation-remote sensing approach to quantify river discharge source waters in a representative headwater basin, the Chamkhar Chhu. Using four years of water isotope and chemistry data together with a Bayesian Monte Carlo mixing model run seasonally in 2016, we find that the Chamkhar Chhu is mostly a rain-dominated basin at the lower elevation of our study domain (2591 m a.s.l.), with peak contributions from snowmelt in the early-monsoon and ice melt in the post-monsoon seasons. The radioactive tritium isotope shows glacier ice at the terminus was formed before the 1960s bomb spike while late monsoon groundwater and river water samples are sourced from mostly newer water inputs. An overall decreasing trend in the minimum snow and ice cover extent maps produced using MODIS Terra data from 2000-2017 suggest a lessening of cryospheric water resource availability in the basin, although this time series is short compared to the timescale of atmospheric-oceanic oscillations controlling snowfall. While decreasing snow and ice resources will likely lead to changing melt water contributions to river discharge, the overall impact on the water resources may be buffered by rainfall contributions as previous studies forecast an increase in precipitation for the region that will likely make up for lower melt water inputs.

Trend analysis of monsoon season monthly rainfall of Nagwan watershed

The daily rainfall data for a period of 32 years from 1983-2014 of gauging station located in Nagwan watershed of Hazaribagh, Jharkhand were analyzed to study variation of monsoon months and monsoon season rainfall distribution pattern and its trend. The monsoon months and monsoon season rainfall series from daily data were developed. The mean, standard deviation, coefficient of variation, coefficient of skewness and kurtosis of monsoon months and monsoon season rainfall series were calculated. The percentage contributions of monthly rainfall to monsoon season rainfall values were also calculated. Frequency distributions of monsoon months and monsoon season rainfall were developed. The monsoon months and monsoon season rainfall time series were splitted in four sub-periods viz. 1983-1989, 1990-1999, 2000-2009 and 2010-2014. The difference in mean of monsoon months and monsoon season rainfall were tested by student t-test at 5% level of significance. The trend in monthly and monsoon season rainfall were tested by Mann-Kendall rank correlation test, Sen's slope estimator method and by regression test for linear trend. The value of Mann-Kendall statistic is negative for June, July, August, September and Monsoon season rainfall indicating a falling trend. However trend is not significant in all the cases at 5% significance level. Rising trend for the month of August and falling trend in case of June, July, September and Monsoon season are observed by Sen’s method. No significant rising or falling trend on the regression slope for all the time series is observed at 5% level of significance.

On the linkage between extreme rainfall and the Madden–Julian Oscillation over the Indian region

AbstractThe relationship between extreme rainfall events (ERE) and the Madden–Julian Oscillation (MJO) over the Indian Subcontinent is intriguing. In this regard, the study investigates in detail the association between the ERE and the MJO. Daily Tropical Rainfall Measuring Mission (TRMM) data were used for the period 1998–2015. The real‐time multivariate MJO index was applied to classify active and suppressed phases of the MJO. The percentile‐based threshold indices, change in probability, logistic regression models and composite analysis were used to understand the statistical and atmospheric circulation features. The results suggest that the frequency and rainfall contribution of the ERE were found to be higher during the active phases of the MJO across the seasons over the geographically distinct regions. The profound influence of the MJO on the ERE was found during the post‐monsoon over the southern Indian peninsula and Bay of Bengal regions. During the Indian Summer Monsoon (ISM), the prominent signals of the MJO are limited to the south of 20 ° N. The logistic regression and cumulative probability changes affirm the above results. The composite analysis of various diagnostic parameters reveals the background synoptic conditions during the post‐monsoon and the propagation of the Rossby convective lobe during the ISM might facilitate the occurrences of the ERE during the active phases of the MJO. The study highlights the space–time evolution of the ERE and the relative influence of the MJO across the seasons. Besides, its insights have practical implications for the understanding and prediction of sub‐seasonal rainfall extremes over the Indian Subcontinent.

Climate Change Implications for Water Availability: A Case Study of Barcelona City

Barcelona city has a strong dependence on the Ter and Llobregat reservoir system to provide drinking water. One main concern for the next century is a potential water scarcity triggered by a severe and persistent rainfall shortage. This is one of the climate-driven impacts studied within the EU funded project RESCCUE. To evaluate potential drought scenarios, the Hydrologiska Byråns Vattenbalansavdelning (HBV) hydrological model reproduces the water contributions by month that have reached the reservoirs, regarding the accumulated rainfall over each sub-basin, representing the available historical-observed water levels. For future scenarios, we adjusted the input data set using climate projections of rainfall time series data of the project RESCCUE. Local outputs from 9 different climate models were applied to simulate river basins’ responses to reservoirs’ incoming water volume. Analyzing these results, we obtained average trends of the models for each scenario, hypothetical extreme values, and quantification for changes in water availability. Future water availability scenarios for Barcelona central water sources showed a mean decrease close to 11% in comparison with the period 1971–2015, considering the representative concentration pathway 8.5 (RCP8.5) climate change scenario in the year 2100. This research forecasts a slight downward trend in water availability from rainfall contributions from the mid-21st century. This planned future behavior does not mean that the annual water contributions are getting lower than the current ones, but rather, identifies an escalation in the frequency of drought cycles.

Temporal and spatial variations of convection, clouds and precipitation over the Tibetan Plateau from recent satellite observations. Part II: Precipitation climatology derived from global precipitation measurement mission

AbstractThis sequence of papers examines spatio‐temporal variations of precipitation over the Tibetan Plateau (TP) based on satellite observations. Here in Part 2, spatial patterns of seasonal and diurnal variations of precipitation have been examined based on the Global Precipitation Measurement Mission (GPM) and three additional satellite products. The results show a spatial dipole pattern of two distinct seasonalities: The central TP is marked by strong July peaks and exhibits rainfall contributions of the monsoon season (May–September) of more than 70%, whereas northwestern and southern regions of the plateau exhibit significantly smaller amplitudes in the annual cycle. In some southern regions which are characterized by very high summer mean precipitation and more extreme rain rates, winter months (October–April) contribute significantly to the total annual mean precipitation. In addition, there are larger differences in seasonal curves along a west‐to‐east axis, than along a north‐to‐south axis. The spatial patterns of diurnal precipitation over the TP are more complex compared to seasonality and point to multiple components, which construct the regional differences. These show also a seasonal dependence and are characterized by a stronger afternoon to early evening peak (17:00 LST time, 11:00 UTC) and weaker nighttime peak (23:00 LST, 17:00 UTC) during the monsoon season and over the plateau compared to its surroundings. Furthermore, it was shown that convective precipitation during the monsoon season contribute only up to 30% to the total precipitation, whereas more than 70% is produced by the 90th percentile of daily rain rates. An important characteristic of summer precipitation is hence that a significant part of the extreme precipitation is non‐convective. This paper reveals new features of spatial patterns in seasonal and diurnal precipitation and highlights the importance of non‐monsoonal components for seasonal precipitation variations.

Seasonal Shift From Biogenic to Geogenic Fluvial Carbon Caused by Changing Water Sources in the Wet‐Dry Tropics

AbstractThe riverine export of carbon is expected to be driven by changes in connectivity between source areas and streams. Yet we lack a thorough understanding of the relative contributions of different water sources to the dissolved carbon flux, and of the way these contributions vary with seasonal changes in flow connectivity. Here we assess the temporal variations in water and associated dissolved inorganic carbon (DIC) sources and fluxes in a wet‐dry tropical river of northern Australia over two years. We use linear mixing models integrated into a Bayesian framework to determine the relative contributions of rainfall, seasonal wetlands, shallow groundwater, and a deep carbonate aquifer to riverine DIC fluxes, which we relate to the age of water sources. Our results suggest extreme shifts in water and DIC sources between the wet and dry seasons. Under wet conditions, most DIC was of biogenic origin and transported by relatively young water sources originating from shallow groundwater and wetlands. As rainfall ceased, the wetlands either dried out or became disconnected from the stream network. From this stage, DIC switched to a geogenic origin, nearly entirely conveyed via older water sources from the carbonate formation. Our findings demonstrate the importance of changing patterns of connectivity when evaluating riverine DIC export from catchments. This work also illustrates the need to systematically partition DIC fluxes between biogenic and geogenic sources, if we are to quantify how the riverine export of carbon affects net carbon soil storage.

Landslides triggered after the 16 August 2018 Mw 5.1 Molise earthquake (Italy) by a combination of intense rainfalls and seismic shaking

On 16 August 2018, a Mw 5.1 earthquake occurred in the Molise region (Central Italy) during an intense rainfall event which cumulated up to 140 mm in 3 days. Within 5 days after the seismic event, 88 landslides were surveyed and classified in disrupted and coherent as well as in first-time failures and reactivation. As it resulted by the inventorying, most of the surveyed ground effects were represented by coherent landslides involving clays, marly clays, and cover deposits on low dipping slopes. A spatial distribution analysis of landslides in relation to seismic action and rainfall intensity was carried out to evaluate the possible contribution of both the rainfall-induced saturation and the earthquake shaking to landslide triggering. Based on this analysis, in the epicentral area, it is not possible to clearly split the role of seismic and hydraulic destabilising actions, while, at greater distances, the joined contribution of rainfall and earthquake shaking could have promoted slope failures. Comparisons among collected data and existing worldwide catalogues allow to highlight, through the analysis of the spatial distribution of the surveyed landslides, the possible and not negligible effect of soil saturation during the seismic shaking both in epicentral distance vs. magnitude distribution and in number and spatial concentration of triggered ground effects.

Comparative Study of Hydrology and Icemelt in Three Nepal River Basins Using the Glacio-Hydrological Degree-Day Model (GDM) and Observations From the Advanced Scatterometer (ASCAT)

An assessment of the water supply and its seasonal and annual changes over the century in the High Mountain Asia (HMA) region is of increasing interest due to its potential impact on one-sixth of the global population. In order to understand the changing hydrology and snow and ice melt, we used remotely sensed Advanced Sscatterometer (ASCAT) observations of glacier melt (GM) and a physically based gridded Glacio-hydrological Degree-day Model (GDM) in three river basins: Tamor, Trishuli and Marsyangdi. The GDM-estimated contribution of snowmelt, icemelt, rainfall and baseflow in river flows iswas found to be most accurate in the Trishuli River basin, with Nash-Sutcliffe efficiency (NSE) between the estimated and observed discharges of 0.81 and volume differences of -0.5 %, and reasonably accurate in the Tamor River basin, with NSE of 0.69 and volume difference of -7.51 %. Similarly, NSE of 0.81 and volume difference of 4.64 % in Marshyangdi River basin. We find strong similarities in the timing of glacier melting using the GDM and from observations from the ASCAT GM, determining the seasonal start of glacier melting to within 6 days on average. In all basins ASCAT GM observes melting at higher elevations relative to GDM, well within the accumulation zone, average of 5,328 m.a.s.l‬. Systematic differences in glacier melting area determined by modeling and satellite observations indicate ASCAT may have suboptimal resolution, view geometry and/or polarimetry for delineating glacier melting at the process-scale in complex topography, especially in the ablation zone. This is the first step in examining the remote sensing products that could potentially be incorporated into hydrologic models to increase the accuracy of the hydrologic flow as well as the ability to estimate river discharge in other basins with limited data.

Spatiotemporal analysis of extreme indices derived from daily precipitation and temperature for climate change detection over India

The study analysed the spatiotemporal variation in extreme precipitation and temperature at the daily scale across India using eight indices of climate change suggested by the Expert Team on Climate Change Detection and Indices (ETCCDI). For this analysis, latest high-resolution India Meteorological Department (IMD) data for the period 1971–2017 (precipitation) and 1971–2013 (temperature) are used along with global gridded reanalysis products. The trends are evaluated using non-parametric Mann-Kendall (MK) test and regression analysis. At the annual scale, about 13% of the locations indicated significant trend (either increasing or decreasing at 5% significance level) in the index R95p (rainfall contribution from extreme ‘wet days’) while 20% of the locations indicated significant trend in R5p (rainfall contribution from extreme ‘dry days’). For the seasonal analysis (June to September), the corresponding figures are nil and 21% respectively. The number of ‘warm days’ per year increased significantly at 14% of the locations, while the number of ‘cold days’, ‘warm nights’ and ‘cold nights’ per year decreased significantly at several (42%, 34% and 39%) of the locations. The extreme temperature indices for the future (using CanESM2 projected data for RCP8.5 after suitable bias correction) show significant increasing (decreasing) trend in warm days (cold days) in most (49% to 84%) of the locations. Further, most locations (varying from 60 to 81%) show an increasing trend in warm nights and a decreasing trend in cold nights. Similar analysis for the historical and future period are also performed using Climate Prediction Centre (CPC) reanalysis data as the reference and the trends, on comparison with IMD data, seem to be in agreement for temperature extremes but spatially more extensive in case of CPC precipitation extremes.

Understanding the Evolution and Socio-Economic Impacts of the Extreme Rainfall Events in March-May 2017 to 2020 in East Africa

This study aimed at assessing the evolution, distribution and the socio-economic impacts of extreme rainfall over East Africa during the March, April and May (MAM) rainfall season focusing on assessing the trends and contribution of MAM rainfall in mean annual rainfall across the region. It employed Principal Component Analysis (PCA) methods to capture the patterns and variability of MAM rainfall. The PCA results indicated that the first Principal Component (PC) describe 17% of the total variance, while the first six PCs account only 53.5% of the total variance in MAM rainfall, underscoring the complexity of rainfall forcing factors in the region. It has been observed that MAM rainfall accounts about 30% - 60% of the mean annual rainfall in most parts of the region, signifying its importance in agriculture, water, energy and other socio-economic sectors. MAM has been characterized by increasing variability with varying trend patterns across the region. The MAM rainfall trend is not homogeneous across the region; some areas are experiencing a slight decreasing rainfall trend, while other areas are experiencing a slight increasing rainfall trend. The observed trend dynamics is consistent with the global trend patterns in precipitation as depicted in recent Intergovernmental Panel on Climate Change (IPCC) reports. Over the last five years MAM rainfall season have been characterized by record-breaking extremes. On 8th May 2017, Tanga and Mombasa meteorological stations recorded 316 mm and 235.1 mm of rainfall in 24 hours respectively, which are the highest amounts for these respective stations, since their establishment. Record highest 24 hours rainfall amounting to 134.9 mm and 119.4 mm were also observed at Buginyanya and Kawanda meteorological stations in Uganda on 18th March 2018 and 7th May 2020. On 6th May 2020, Byimana meteorological station in Rwanda, also observed 140.6 mm of rainfall in 24 hours, the highest since its establishment. These extremes have caused multiple losses of life and property, and severe damages to infrastructure. Unfortunately, the frequency and intensity of these extremes are projected to increase under a changing regional climate patterns. It is therefore important that more studies are carried out to enhance understanding about the evolution, dynamics and predictability of these extremes in East Africa region.

Spatial and seasonal variation of rainfall contribution by the height spectrum of precipitation systems and associated cloud bulk properties over the South Asia

AbstractThe spatial‐seasonal variation of rainfall contribution by the height spectrum of precipitation systems in terms of maximum echo top height of 20 and 40 dBZ (ETH20 dBZ (max) and ETH40 dBZ (max)) is investigated. The study is carried out during the pre‐monsoon (March–May) and monsoon (June–September) over the continental, coastal and oceanic regions of South‐Asia. For this purpose, 17 years (1998–2014) of TRMM‐PR and 4 years (2007–2010) of CloudSat‐CPR observations are considered. Over the continental (coastal/oceanic) regions, the maximum rainfall contribution is by relatively deeper ETH20 dBZ (max) during the monsoon (pre‐monsoon). During the pre‐monsoon (monsoon), the maximum rainfall contribution by Deep Convective Systems (DCSs) is over the Northern‐Myanmar‐Coast; 55% (Western‐Himalaya‐Indentation; 39%). Over the central Arabian‐Sea and central Bay‐of‐Bengal, rainfall contributions by DCSs are predominantly associated with Tropical Cyclonic Disturbances (TCDs) in the pre‐monsoon season. In terms of ETH40 dBZ (max), the maximum rainfall contribution over the continental region during the pre‐monsoon is by relatively stronger Precipitation Features (PFs) compared to the monsoon. Unlike the other regions, during the pre‐monsoon, over the Western‐Himalaya‐Indentation and Central‐Himalaya‐Foothills, rainfall contribution by Intense Convective Systems (ICSs) is significantly higher compared to DCSs. During the pre‐monsoon (monsoon), the maximum rainfall contribution by ICSs is over the Eastern‐India‐Coast; 35% (Western‐Himalaya‐Indentation; 18%). The rainfall contribution by ICSs during TCDs is insignificant. During both the seasons, the regions of high rainfall contribution by ICSs, DCSs, and shallow PFs are associated with relatively higher (≥400 mg‐m−3), moderate (300–350 mg‐m−3), and low (<150 mg‐m−3) Cloud Ice Water Content (CIWC) in the mixed‐phase region, respectively, suggesting a strong, moderate and weak mixed‐phase processes involved in the respective PFs. TCDs enhance the occurrence of DCSs with moderate CIWC in mixed‐phase region and leading to enhanced rainfall contribution by them over the active cyclone regions.

Discrimination of soil losses between ridge and furrow in longitudinal ridge-tillage under simulated upslope inflow and rainfall

Longitudinal ridge-tillage greatly enhances hillslope soil erosion due to increased flow concentration in furrows and sediment delivery from ridge sideslopes. Currently, contributions of upslope inflow and rainfall to soil loss and identification of sediment sources in a ridge-furrow system are still unclear. A set of experiments on 10-m long, 2-m wide field runoff plots at a 5° slope gradient were conducted in the Chinese Mollisol region to quantify the effects of upslope inflow and rainfall on hillslope erosion and to discriminate sediment contributions between ridges and furrows in a longitudinal ridge-tillage system. The experimental treatments included five upslope inflow rates alone (10, 20, 30, 40 and 50 L min−1), two rainfall intensities alone (50 and 100 mm h−1) and the five inflow rates combined with the two rainfall intensities. A stereoscopic photogrammetry method was used to measure micro-topographic conditions before and after each run. The results showed that, compared with the inflow-only treatments, soil losses increased by 1.4–5.2 times and 2.5–14.0 times under the combined treatments of the five inflow rates and two rainfall intensities, respectively. The contributions of the synergistic effects increased with the increase of rainfall intensity. Moreover, in the five upslope inflow-only treatments, soil erosion mainly occurred in the bottom of furrows and ridge toe slopes; while for the combined treatments, ridge sideslope erosion dominated as soil loss from ridge areas accounted for 51.3 %–60.9 % and 53.0 %–61.8 % for the 50 and 100 mm h−1 rainfall intensities, respectively. Therefore, ridge sideslope erosion may be the main sediment source in the longitudinal ridge-tillage system under the bare conditions.