Moderate Rainfall Events Research Articles

Urban Flood Modeling Application: Assess the Effectiveness of Building Regulation in Coping with Urban Flooding Under Precipitation Uncertainty

This research evaluates the effectiveness of planning and building regulations in coping with urban flooding under different precipitation scenarios. Accordingly, the study simulated seven alternative scenarios considering the variations of precipitation, plot coverage regulations, and Low Impact Development (LID) options. The study utilized open-source geospatial software to model different surface runoff scenarios. Then the effectiveness of those seven alternatives was assessed by utilizing the Analytical Hierarchy Process (AHP) technique to evaluate their sustainability in urban design. The results revealed that the plot coverage regulations are effective in managing floods during average rainfall events, and LID-based infrastructure solutions are effective during moderate rainfall events. Nevertheless, none of these solutions were solely adequate during extreme rainfall events. Regardless of the response to extreme rainfall occurrences, the practitioners’ opinion was in favour of green roof adoption and plot coverage regulation considering their effectiveness in managing more frequent average rainfall events, and the overall sustainability in maintaining the balance of urban hydrological pathways. Accordingly, the findings of the study can be utilized as a guide to the decision-making process in urban planning and design, and to formulate sustainable planning regulations and guidelines to cope with urban flooding under the precipitation uncertainty.

A MESO-scale Rain gauge NETwork-MESONET over Mumbai: Preliminary results and applications

Mumbai, the compact megacity, the economic capital of India, is highly vulnerable to severe weather conditions, particularly related to the rainfall phenomenon. A MESO-scale rain gauge NETwork (MESONET) comprises 131 rain gauges scattered over the Mumbai metropolitan region is established to have instantaneous rainfall information. A real-time web-based rainfall data portal is set up as a public informative/awareness system that would help the public to cope with unanticipated situations caused by massive rainfall events. In this work, we provide the rationale of Mumbai MESONET and preliminary results from the observations during July–October 2019.High-resolution MESONET rainfall data are analyzed to examine the mean and associated small-scale spatiotemporal variability of rainfall over Mumbai. The results depict that the maximum contribution of rainfall is from low to moderate and heavy rainfall events. The prevalent occurrence of prolonged rainfall events of moderate to high intensity during mid-night and early morning hours is attributed to the diurnal variability of events duration. It is observed that heavy rainfall events (64–124 mm/day) occur at a sub-daily scale. Correlogram analysis of rainfall further reveals the good spatial coherence in the spatial variability of rainfall even at sub-daily scales.

The application of generalized additive models (GAMs) for assessing the teleconnection of ENSO and IOD with monsoon rainfall variability over Krishna river basin, India

The present study examines the teleconnection of ENSO andIOD with monsoon rainfall (MN) and low, moderate and heavy rainfall events (LREs, MREs and HREs) over the Krishna river basin, using generalized additive models (GAMs) with suitable distribution. The outputs of GAMs indicate that, Poisson distribution is superior to the other distributions in assessing the teleconnection of ENSO-MN-IOD in the study area. Further, study resultsshowed that ENSO and IOD has significant (p < 0.001) non-linear responses to theLREs, MREs,HREs and MN. The influence of IOD on MN, LREs, MREs and HREs found positive on some parts, while negative on the other parts of the study area (i.e. heterogeneous in nature). While, ENSO has consistent negative influence on MN, LREs, MREs and HREsin the study area. Furthermore, La Niña and El Niño had positive and negative influenceon the MN, LREs, MREs and HREs respectively. The study outcomes will help the hydro-meteorologist and water related policy makers in modeling the impact of monsoon rainfall system on water, agriculture and allied sectors.

Effects of thinning and understory removal on the soil water-holding capacity in Pinus massoniana plantations

Forest management practices play an important role in regulating the soil water-holding capacity of plantation. However, most studies focus on soil water dynamics present during large-scale forest loss and afforestation events, while little is known about how soil water under different forest management practices responds to rainfall events and which factors mainly regulate soil water-holding capacity. In this study, a stable hydrogen isotope was used to explore the contribution of three natural rainfall events (8.9, 13.3 and 67.7 mm) to soil water (CRSW) in a Pinus massoniana plantation under four forest management practices (no thinning (NTN), understory removal (USR), light-intensity thinning (LIT) and heavy-intensity thinning (HIT)) in the Three Gorges Reservoir Area of the Yangtze River Basin in China. Furthermore, a structural equation model was employed to determine the effects of vegetation biomass and soil properties on the CRSW. The results showed that plantation soil under different forest management practices exhibited different water-holding capacities. Following light (8.9 mm) and moderate (13.3 mm) rainfall events, the CRSW in the HIT stand was slightly higher than that in the other stands. Following heavy (66.7 mm) rainfall event, the CRSW of most layers in USR stand was not different from the other three stands, while the CRSW in the LIT and NTN stands was significantly higher than that in the HIT stand in the 0–100 cm soil layers, suggesting that soil in the LIT and NTN stands had a greater water-holding capacity than that in the HIT stand. In addition, soil properties were the main factors directly affecting the CRSW, explaining 60% and 37% of the variation in the CRSW on the first and seventh days after heavy rainfall, respectively. Overall, compared to the HIT stand, the LIT and NTN stands showed greater capacity in retaining rainwater. Therefore, under expected global changes with frequent occurrences of extreme precipitation events, methods involving light-intensity and no thinning should be employed to build up soil and water conservation functions, which will be critical for keeping water-holding capacity and moderating floods.

Soil moisture responses under different vegetation types to winter rainfall events in a humid karst region.

Soil moisture influences plant growth and hydrological processes. Studying the response characteristics of soil moisture to winter rainfall under different vegetation types in humid karst areas is important for optimizing the restoration patterns in these areas. To this end, we monitored the soil moisture content of arable, grassland, shrub, and forest areas in the karst of Guanling County, Guizhou Province, China, at 10-min intervals. The rainfall threshold for the soil moisture response was the smallest in grassland areas. Under different vegetation types, the soil moisture increase tended to be maximized in light-rainfall events and minimized in medium-rainfall events. Moreover, the increase in soil moisture in the profile under the different vegetation types generally decreased with increasing soil depth during light and rainstorm events, but the opposite variation pattern was observed during moderate-rainfall events. In different rainfall events, the soil moisture recharge and soil moisture decrease were greatest in grassland areas. Among the vegetation types, shrubs maintained the highest mean soil moisture content in winter, with a higher recharge and a smaller decrease in soil moisture. This suggests that shrubs can better maintain their soil moisture content in winter than other vegetation types, which has implications for the selection of regional vegetation restoration patterns.

A device for rainfall simulation in geotechnical centrifuges

Rainfall-induced slope instabilities are ubiquitous in nature, but simulation of this type of hazards with centrifuge modelling still poses difficulties. In this paper, we introduce a rainfall device for initiating slope failure in a medium-sized centrifuge. This rainfall system is simple, robust and affordable. An array of perforated hoses is placed close above the model slope surface to generate the raindrops. The rainfall intensity depends on the centrifuge acceleration and the flow rate of the water supply, which is controlled by the size and number of the tiny pinholes in the hose walls. The rainfall intensities that are tested range from 2.5–30 mm/h, covering the intensity range of moderate, heavy and torrential rainfall events. Our model test with rainfall-induced slope failure shows that this system is capable of generating relatively uniform rainfall of wide intensities and leads to various patterns of slope failure.

Extreme changes in salinity drive population dynamics of Catostylus mosaicus medusae in a modified estuary

Modifications to estuaries through the construction of barrages alter the natural dynamics of inhabitant species by controlling freshwater inputs into those systems. To understand the effects of modified freshwater flows on a native scyphozoan jellyfish, Catostylus mosaicus, and to identify the environmental drivers of medusa occurrence, we analysed a 20-year observational dataset composed of 11 environmental variables and medusa presence/absence from 15 sampling stations located below the Fitzroy Barrage, in the Fitzroy River, Queensland. Major decreases in salinity (minimum salinity 0) occurred approximately 16 times during the 20-year period and medusae disappeared from the estuary following every major freshwater flow event. Salinity was identified as the most influential variable contributing to variation in the number of upper estuary sites reporting jellyfish. We then ran two laboratory experiments to test the following hypotheses: (i) prolonged decreases in salinity impair survival, pulsation, and respiration rates of C. mosaicus medusae; and (ii) transient decreases temporarily impair pulsation and respiration but medusae recover when salinity returns to normal levels. Medusae were unable to survive extended periods at extreme low salinities, such that they would experience when a barrage opens fully, but had significantly higher survival and recovery rates following smaller, transient changes to salinity that might occur following a moderate rainfall event. This demonstrates for the first time that modification of freshwater flow by a barrage regulates the population dynamics of an estuarine jellyfish, and highlights the need for robust, long term datasets, and to firmly embed experimental approaches in realistic ecological contexts.

Pathogenic Leptospira and water quality in African cities: A case study of Cotonou, Benin

Leptospirosis is a waterborne zoonosis (60,000 infections and 1 million deaths annually). Knowledge about the disease in the urban context is surprisingly rare, especially in Africa. Here, we provide the first study of leptospires in waters within an African city. A simple centrifugation-based method was developed to screen waterborne leptospires from remote or poorly areas. Major ions, trace elements, stable isotopes and pathogenic Leptospira were then seasonally investigated in 193 water samples from three neighborhoods of Cotonou (Benin) with different socio-environmental and hydrographic characteristics. Firstly, no leptospire was detected in tap waters. Secondly, although surface contamination cannot be excluded, one groundwater well was found leptospire positive. Thirdly, pathogenic Leptospira mainly contaminated surface waters of temporary and permanent ponds (9.5% and 27.3% of total prevalence, respectively). Isotopic signatures suggest that leptospires occurred in pond waters formed at the beginning of the rainy season following low to moderate rainfall events. Nevertheless, Leptospira-containing waters possess physico-chemical characteristics that are similar to the spectrum of waters sampled throughout the three sites, thus suggesting that Cotonou waters are widely compatible with Leptospira survival. The frequent contact with water exposes Cotonou inhabitants to the risk of leptospirosis which deserves more attention from public health authorities.

Comparison of Soil Erosion Control by Mulch and Cultivated Grass

Soil erosion has deteriorated water quality and caused land degradation. As human industrialization quickens, the effects of soil erosion are getting worse. Therefore, it is essential to have an effective mitigation measure at hand to solve this problem. In this research, two types of erosion control methods were compared to determine their effectiveness in controlling soil erosion. The two methods used were mulch made from dried grass clippings and grass cultivation grown with Axonopus compressus or more commonly known as cow grass. The plots were placed under five rainfall events together with a control plot. The runoff volume, turbidity and total suspended solids (TSS) from the plot discharges were tested and compared. The effectiveness of each erosion control method under different rainfall conditions were also evaluated. Results indicated that the mulch plot produced a lower runoff volume but the grass plot did manage to improve performance over time. The turbidity of both plots were similar. The TSS produced by the grass plot was lower than the mulch plot in 4 out of the 5 testing periods. The grass plot also performed better in longer duration and high intensity rainfall events. The mulch was able to produce similar results with the grass in short duration, low or moderate intensity rainfall events. As a conclusion, the grass cultivation is a more effective erosion control method when compared to the mulch.

Individual Rainfall Change Based on Observed Hourly Precipitation Records on the Chinese Loess Plateau from 1983 to 2012

The magnitude and spatiotemporal distribution of precipitation are the main drivers of hydrologic and agricultural processes in soil moisture, runoff generation, soil erosion, vegetation growth and agriculture activities on the Loess Plateau (LP). This study detects the spatiotemporal variations of individual rainfall events during a rainy season (RS) from May to September based on the hourly precipitation data measured at 87 stations on the LP from 1983 to 2012. The incidence and contribution rates were calculated for all classes of rainfall duration and intensity to identify the dominant contribution to the rainfall amount and frequency variations. The trend rates of regional mean annual total rainfall amount (ATR) and annual mean rainfall intensity (ARI) were 0.43 mm/year and 0.002 mm/h/year in the RS for 1983–2012, respectively. However, the regional mean annual total rainfall frequency (ARF) and rainfall events (ATE) were −0.27 h/year and −0.11 times/year, respectively. In terms of spatial patterns, an increase in ATR appeared in most areas except for the southwest, while the ARI increased throughout the study region, with particularly higher values in the northwest and southeast. Areas of decreasing ARF occurred mainly in the northwest and central south of the LP, while ATE was found in most areas except for the northeast. Short-duration (≤6 h) and light rainfall events occurred mostly on the LP, accounting for 69.89% and 72.48% of total rainfall events, respectively. Long-duration (≥7 h) and moderate rainfall events contributed to the total rainfall amount by 70.64% and 66.73% of the total rainfall amount, respectively. Rainfall frequency contributed the most to the variations of rainfall amount for light and moderate rainfall events, while rainfall intensity played an important role in heavy rainfall and rainstorms. The variation in rainfall frequency for moderate rainfall, heavy rainfall, and rainstorms is mainly affected by rainfall duration, while rainfall event was identified as a critical factor for light rainfall. The characteristics in rainfall variations on the Loess Plateau revealed in this study can provide useful information for sustainable water resources management and plans.

Parameter estimation of a dual-pol radar rain rate estimator with truncated paired data

Abstract This study proposes a new method for estimating the parameters of a radar rain rate estimator, particularly of the dual-pol radar. The proposed method is similar to the probability matching method (PMM), except for being based on truncated data pairs. A truncation value is introduced to the log-transformed data in order to remove those in the low rain rate zone as well as to introduce Gaussian distribution. The parameters are then estimated by comparing the first- and second-order moments. The proposed method is applied to a total of six rainfall events observed by the Beaslesan Radar in Korea from 2014 to 2017. Summarizing the results, first, the truncation value should be applied to the horizontal reflectivity (dBZh) data. In this case only, the other two data, the rain rate (dBR) and the differential reflectivity (dBZdr), follow the Gaussian distribution well. It is also important to consider rather severe rainfall events for the parameter estimation. The parameters for only the severe rainfall events are all estimated rather reasonably. On the other hand, for the other moderate and light rainfall events, the parameters are estimated as being rather far from their normal ranges. This is mainly due to the relatively small variance of dBR compared to that of dBZh. That is, the variance of dBR is found to be greatly dependent on the peak rain rate, but the variance of dBZh remains almost unchanged, regardless of the peak rain rate. As a result, the peak rain rate plays a dominant role in the reasonable parameter estimation. These findings are also consistent with many previous studies.

Effects of rainfall on thermal stratification and dissolved oxygen in a deep drinking water reservoir

AbstractThermal stratification is crucial for water quality and ecological processes in deep lakes and reservoirs and can be substantially affected by meteorological and hydrological processes in the catchment. However, how thermal stratification responds to rainfalls of different intensities and changing hydrological processes has not been documented very well. Here, high frequency water column profiles at three stations in a large subtropical deep reservoir (Lake Qiandaohu, China) in 2017 were used to elucidate the impacts of rainfall on lake physical process and chemical environment. The impact of rainfalls on the thermal stratification and dissolved oxygen in riverine zone was more impressive than that in transitional and lacustrine zones. The effect on thermal stratification by rainfall was largely affected by the magnitude of rainfall. Moderate and heavy rainfall events could reduce the thermal stability of water column, deepen the mixing layer depth, and shape the thermocline, resulting from decrease of surface water temperature and increased inflows. While rainstorms could totally break up thermoclines in the riverine zone by high volume inflow flushing. In addition, we found that the hypoxia and anoxia initial depths increased during rainfall events in this reservoir, which were well related to the changes of mixing layer depths. This research highlights that quantifying the effects of rainfalls on thermal stratification and dissolved oxygen will be beneficial for optimizing reservoir management.

Assessment of satellite precipitation product estimates over Bali Island

Satellite precipitation product estimates (SPPEs) provide rainfall data on regional and global scales and have the potential to be applied in various fields. Several satellite precipitation estimates are available for their various features in retrieval algorithms, used sensor instrument, spatial–temporal resolution, and coverage area. Global Satellite Mapping of Precipitation (GSMaP), Integrated MultisatellitE Retrievals (IMERG), and Climate Hazards Group Infrared Precipitation with Station (CHIRPS) are global coverage precipitation datasets with high spatial resolution (0.1°–0.05°) and high temporal resolution (from 30 min to daily updates). The objective of this study was to assess the performance of GSMaP, IMERG, and CHIRPS over Bali Island from 2015 to 2017 in terms of ground rain gauge data over a high density of rain gauge stations (27 in-situ rain gauges) and at various elevations, rainfall intensities, and temporal scales (i.e., daily, penta-days, monthly, and seasonal). A traditional point-to-pixel-based method along with a new introduced continuous, categorical, and volumetric statistical indices comparison approach were implemented to evaluate satellite products. The assessment results demonstrated that IMERG products achieved the highest performance on daily, penta-day, and seasonal time scales, whereas CHIRPS outperformed the other two products on the monthly time scale. Moreover, IMERG was more efficient in detecting rainfall events at different altitudes, but it tended to overestimate rainfall events at high altitudes. With respect to their abilities to detect rainfall events, GSMaP, IMERG, and CHIRPS tended to underestimate the frequency of light rainfall events (0–1 mm/day) and heavy rainfall events (>50 mm/day) but overestimate the frequency of moderate rainfall events (5–10 mm/day). Our result not only highlight IMERG products exhibited better performance in comparison to GSMaP and CHIRPS in Bali Island but also recommend that further improvement on the precipitation estimate algorithm is required by considering complex terrain over small island in the maritime continent area.

Precursors of northeast monsoon rainfall variability during extreme epochs of the global warming era

AbstractThe smoothed time series of northeast monsoon rainfall over south peninsular (SP) India has revealed two extreme active epochs (1877–1887 and 2005–2015) and two extreme weak epochs (1899–1909 and 1980–1990) during 1871–2016. Only the recent two epochs 1980–1990 and 2005–2015 were chosen due to data constraints. For these two epochs, the distribution of zonal wind pattern at the 850 and 200 hPa levels, latent heat flux, vertical shear in the zonal wind between 850 and 200 hPa, sea surface temperature and outgoing long wave radiation (OLR) were studied. The vertical profile of zonal wind over the mean position of the subtropical westerly jet and the maximum wind reversal were also analysed. Further, the frequencies of dry days, little rainfall days (0–20 mm), moderate rainfall days (20–60 mm), heavy rainfall days (60–100 mm) and very heavy rainfall days (>100 mm) were evaluated. SP India has experienced active/weak monsoon conditions every one to two decades alternately. An active monsoon epoch shows a higher north–south temperature gradient over the Bay of Bengal than a weak monsoon epoch. An upper level subtropical westerly jet over north India, strong tropical easterlies in the lower troposphere and low vertical shear in the zonal wind over the Bay of Bengal were observed during the active epoch, which facilitates the transportation of good amounts of moisture to SP India. The low OLR values over SP India in the active monsoon epoch indicate more convective activity over that region. Enhanced rainfall activity over SP India in the active monsoon epoch is due to the enhanced frequency of very heavy, heavy, moderate and little rainfall events and the reduced frequency of dry days.

Integrated Correction Algorithm for X Band Dual-Polarization Radar Reflectivity Based on CINRAD/SA Radar

The values of ratio a of the linear relationship between specific attenuation and specific differential phase vary significantly in convective storms as a result of resonance scattering. The best-linear-fit ratio a at X band is determined using the modified attenuation correction algorithm based on differential phase and attenuation, as well as the premise that reflectivity is unattenuated in S band radar detection. Meanwhile, the systemic reflectivity bias between the X band radar and S band radar and water layer attenuation (ZW) on the wet antenna cover of the X band radar are also considered. The good performance of the modified correction algorithm is demonstrated in a moderate rainfall event. The data were collected by four X band dual-polarization (X-POL) radar sites, namely, BJXCP, BJXFS, BJXSY, and BJXTZ, and a China’s New Generation Weather Radar (CINRAD/SA radar) site, BJSDX, in Beijing on 20 July 2016. Ratio a is calculated for each volume scan of the X band radar, with a mean value of 0.26 dB deg−1 varying from 0.20 to 0.31 dB deg−1. The average values of systemic reflectivity bias between the X band radar (at BJXCP, BJXFS, BJXSY, and BJXTZ) and S band radar (at BJSDX) are 0, −3, 2, and 0 dB, respectively. The experimentally determined ZW is in substantial agreement with the theoretically calculated ones, and their values are an order of magnitude smaller than rain attenuation. The comparison of the modified attenuation correction algorithm and the empirical-fixed-ratio correction algorithm is further evaluated at the X-POL radar. It is shown that the modified attenuation correction algorithm in the present paper provides higher correction accuracy for rain attenuation than the empirical-fixed-ratio correction algorithm.

Quantifying the response of potential flooding risk to urban growth in Beijing

Global urban growth leads to a great increase in the impervious surface area (ISA) such as roads, plazas, airports, and parking lots, and consequently reshapes hydrological regimes in urban basins. Beijing, the capital of China, has experienced rapid urban growth since the 1980s. However, the spatial-temporal variability of the ISA and its impact on flooding risk are unclear. This study monitored urban growth (i.e., the evolution of the ISA) in Beijing for the period of 1980–2015 based on Landsat data, and identified the response of surface runoff yield using a land-surface hydrological model. The modeling at a relatively high spatial resolution (~6 km) was driven with retrieved long-term ISA dynamics, Global LAnd Surface Satellite (GLASS) product, and climate forcings. The results show that the impervious surface fraction (ISF) in Beijing increased from 8.73% (1448.16 km2) in 1980 to 22.22% (3685.92 km2) in 2015. With a demarcation at around the year 2000, the ISA growth presents a new pattern with a northeast-southwest direction from the Core Functional Zone (Core-Zone). Due to the ISA expansion, the simulated runoff coefficient in 2010 is approximately doubled compared to that of 1980. We identified an ISF threshold of approximately 6%, beyond which every 1% increase in the ISF may increase the surface runoff by approximately 5.51 mm/year, and thereby poses a high potential flooding risk even under a moderate rainfall event. In four typical historical storms, the sensitivity coefficients of surface runoff to precipitation and ISF were 0.97 and 0.63, respectively, indicating impervious surfaces dramatically enhanced the potential flooding risk. Our findings have implications for urban planning and the construction of sponge city in Beijing.

Modeling the evolution of soil structural pore space in agricultural soils following tillage

Surface soil structure and pore space are very responsive to both natural and anthropogenic impacts such as rainfall or tillage. These changes affect the soil hydraulic properties as well as the soil water budget. Despite available theories and evidence on the nature of these changes, efforts to capture the temporal dynamics of soil pore size distribution (PSD) and incorporate the derived hydraulic properties in modeling studies are quite rare. The objective of this paper is to examine the suitability of an existing pore evolution model to capture the evolution of soil PSD using water retention parameter (WRP) data sets from around the world. The physical processes governing the evolution of soil PSD are incorporated in the coefficients of the pore evolution model. The applicability of the model to predict the evolution of PSD is discussed and evaluated for two cases (1) when there is a change in tillage regime, and (2) as a novel undertaking, for the months following tillage operations. For the second case, the model is also evaluated for the assumption that the WRPs for the intermediate stages following tillage is not known. This enables us to predict the effects of tillage on soil PSD at a given time even without WRP measurements at all stages. Overall, it is seen that the model and its coefficients are adequate in estimating the overall reduction in porosity and loss of inter-aggregate pores (corresponding to pressure head range from 0 to 330 cm) that are characteristic after tillage operations for both scenarios. In most cases, there is a good agreement between the observed and predicted values indicated by the r2 and RMSE values. The model seems to be less suitable for pores with radii ≤10 μm in some cases, especially for intense rainfall scenarios which may lead to rapid aggregate breakdown and formation of finer pores at a faster rate in comparison to moderate rainfall events. As a solution, we may provide more recent initial conditions for initial PSD to the model following heavy rainfall events and continue our simulations from there to better capture the effects of rainfall. The main limitation for the application of the model is, however, the lack of adequate datasets to validate and calibrate it for different management practices, soil types, and climate regimes.

The effects of topography on aboveground biomass and soil moisture at local scale in dryland grassland ecosystem, China

Water is the primary limiting factor for grassland vegetation in dryland regions. Topography is considered to play an important role in the distribution of soil moisture, which will significantly affect grassland ecosystems. To examine the response of soil water content (SWC) and aboveground biomass (AGB) of grassland vegetation to precipitation patterns and topography, a 6-year investigation was conducted during the period from 2012 to 2017 in a semiarid steppe of Inner Mongolia, China. The study area was divided into three parts based on the landscape position, i.e., top area (TA), slope area (SA) and bottom area (BA). The results suggested that SWC and AGB would be significantly affected by topography and precipitation patterns. A significant negative relationship was found between the SWC and the altitude of the sampling sites. In the dryer years (2013–2017), the AGB of the BA was significantly higher than that of the SA and TA. However, a non-significant difference was found for the AGB values between the three landscape positions in the wetter year (2012). During the growing season, variation of AGB and SWC was similar in 2014 but differed in 2015. AGB exhibited a significant positive relationship with SWC above a minimum value. Precipitation significantly affected the AGB of grassland, and moderate rainfall events were more effective than light rainfall events for grassland vegetation. Moreover, the distribution of species varied in different areas, which may result in the differences in the responses of AGB to soil moisture and precipitation. This study clarifies the effects of micro-topography on soil moisture and grassland ecosystems at a local scale in dryland regions, which provides useful information for grassland ecosystem management.

Evolution of extreme rainfall events over Indo-Gangetic plain in changing climate during 1901–2010

Due to climate variability and climate change there is an increase in magnitude and frequency of extreme precipitation events. During the last few decades these extreme rainfall events have been increased in global as well as on regional scale. Our climate is very much affected by the changes in frequency of extreme rainfall events. Particularly, variability of extreme rainfall events has been studied over one of the most valuable Indian region i.e. over Indo-Gangetic plain (IGP). Long term trend in extreme events has been analyzed with the help of IMD classification. The classification is considered for moderate rain (2.5–64.4 mm; category I), heavy rain (64.5–124.4 mm; category II) and very heavy rain (124.5 mm or more; category III) and the categorization of rainfall events is based on daily rainfall for the period 1901–2010 during Indian summer monsoon (JJAS). The significant long term trend in frequency of extreme rainfall events is analyzed using the statistical test. Long term trend analysis shows the significant decreasing trend for categories II and III. However, an increasing rainfall frequency is observed for moderate rainfall events (category I) during the considered period. A significant interannual and inter-decadal fluctuation in rainfall frequency and magnitude were observed over IGP. Events of moderate and heavy rainfall increases during the withdrawal period of Indian summer monsoon, which might contribute in several cases of flood in the region of IGP. In term of distribution and contribution of rainfall in agriculture area categories I and II, rainfall events are more important but changes in rainfall pattern may lead to flood and drought risk over IGP. The policy making decision for disaster risk and food security should be based on spatial as well as temporal variability of rainfall pattern over IGP region.

Oceanic Forcing on Interannual Variability of Sahel Heavy and Moderate Daily Rainfall

AbstractThis article analyzes SST remote forcing on the interannual variability of Sahel summer (June–September) moderate (below 75th percentile) and heavy (above 75th percentile) daily precipitation events during the period 1981–2016. Evidence is given that interannual variability of these events is markedly different. The occurrence of moderate daily rainfall events appears to be enhanced by positive SST anomalies over the tropical North Atlantic and Mediterranean, which act to increase low-level moisture advection toward the Sahel from the equatorial and north tropical Atlantic (the opposite holds for negative SSTs anomalies). In contrast, heavy and extreme daily rainfall events seem to be linked to El Niño–Southern Oscillation (ENSO) and Mediterranean variability. Under La Niña conditions and a warmer Mediterranean, vertical atmospheric instability is increased over the Sahel and low-level moisture supply from the equatorial Atlantic is enhanced over the area (the reverse is found for opposite-sign SST anomalies). Further evidence suggests that interannual variability of Sahel rainfall is mainly dominated by the extreme events. These results have implications for seasonal forecasting of Sahel moderate and heavy precipitation events based on SST predictors, as significant predictability is found from 1 to 4 months in advance.