Net Rainfall Research Articles

Prediction of streamflow from the set of basins flowing into a coastal bay

Abstract. Many coastal basins of the Brittany peninsula (France) display a high level of nitrate pollution, nine of them highlighted by the European Commission since 2007, as causing algal blooms in several coastal bays. To precisely diagnose and solve this issue the fluxes of every contributing basin have to be considered. However, this faces a strong data-scarce situation as most of the basins are ungauged. In this context, we propose to transpose hydrological information from one gauged basin to neighbouring points of interest. The methodology uses a simple geomorphology-based transfer function on the gauged basin, which allows assessment of the net rainfall time series through the de-convolution of the gauged discharge series. This net rainfall is then transposed and convoluted on the ungauged basin using its own transfer function in order to estimate discharge. This approach enables the quantification of the whole volume of freshwater entering the controversial Saint-Brieuc Bay.

Reconfiguring agriculture through the relocation of production systems for water, environment and food security under climate change

SUMMARYThe prospect of climate change has revived both fears of food insecurity and its corollary, market opportunities for agricultural production. In Australia, with its long history of state-sponsored agricultural development, there is renewed interest in the agricultural development of tropical and sub-tropical northern regions. Climate projections suggest that there will be less water available to the main irrigation systems of the eastern central and southern regions of Australia, while net rainfall could be sustained or even increase in the northern areas. Hence, there could be more intensive use of northern agricultural areas, with the relocation of some production of economically important commodities such as vegetables, rice and cotton. The problem is that the expansion of cropping in northern Australia has been constrained by agronomic and economic considerations.The present paper examines the economics, at both farm and regional level, of relocating some cotton production from the east-central irrigation areas to the north where there is an existing irrigation scheme together with some industry and individual interest in such relocation. Integrated modelling and expert knowledge are used to examine this example of prospective climate change adaptation. Farm-level simulations show that without adaptation, overall gross margins will decrease under a combination of climate change and reduction in water availability. A dynamic regional Computable General Equilibrium model is used to explore two scenarios of relocating cotton production from south east Queensland, to sugar-dominated areas in northern Queensland. Overall, an increase in real economic output and real income was realized when some cotton production was relocated to sugar cane fallow land/new land. There were, however, large negative effects on regional economies where cotton production displaced sugar cane. It is concluded that even excluding the agronomic uncertainties, which are not examined here, there is unlikely to be significant market-driven relocation of cotton production.

Earth Observation Based Assessment of the Water Production and Water Consumption of Nile Basin Agro-Ecosystems

The increasing competition for water resources requires a better understanding of flows, fluxes, stocks, and the services and benefits related to water consumption. This paper explains how public domain Earth Observation data based on Moderate Resolution Imaging Spectroradiometer (MODIS), Second Generation Meteosat (MSG), Tropical Rainfall Measurement Mission (TRMM) and various altimeter measurements can be used to estimate net water production (rainfall (P) > evapotranspiration (ET)) and net water consumption (ET > P) of Nile Basin agro-ecosystems. Rainfall data from TRMM and the Famine Early Warning System Network (FEWS-NET) RainFall Estimates (RFE) products were used in conjunction with actual evapotranspiration from the Operational Simplified Surface Energy Balance (SSEBop) and ETLook models. Water flows laterally between net water production and net water consumption areas as a result of runoff and withdrawals. This lateral flow between the 15 sub-basins of the Nile was estimated, and partitioned into stream flow and non-stream flow using the discharge data. A series of essential water metrics necessary for successful integrated water management are explained and computed. Net water withdrawal estimates (natural and humanly instigated) were assumed to be the difference between net rainfall (Pnet) and actual evapotranspiration (ET) and some first estimates of withdrawals—without flow meters—are provided. Groundwater-dependent ecosystems withdraw large volumes of groundwater, which exceed water withdrawals for the irrigation sector. There is a strong need for the development of more open-access Earth Observation databases, especially for information related to actual ET. The fluxes, flows and storage changes presented form the basis for a global framework to describe monthly and annual water accounts in ungauged river basins.

Estimating groundwater recharge and evapotranspiration from water table fluctuations under three vegetation covers in a coastal sandy aquifer of subtropical Australia

• We estimated groundwater recharge and ET g under three vegetation covers. • Depth-dependent S y were determined under rising and falling water table conditions. • Lower forest recharge was due to higher interception and reduced recharge capacity. • ET g was controlled by meteorological drivers but mediated by depth to water table. To evaluate potential hydrological impacts of changes in vegetation over a shallow sandy aquifer in subtropical Australia, we estimated groundwater recharge and discharge by evapotranspiration ( ET g ) under three vegetation covers. Estimates were obtained over two years (November 2011–October 2013) using the water table fluctuation method and the White method, respectively. Depth-dependent specific yields were determined for estimation of recharge and ET g . Our results show that the average annual gross recharge was largest at the sparse grassland (∼52% of net rainfall), followed by the exotic pine plantation (∼39% of net rainfall) and then the native banksia woodland (∼27% of net rainfall). Lower recharge values at forested sites resulted from higher rainfall interception and reduced storage capacity of the vadose zone due to lower elevations when the water table approaches the soil surface. During 169 rain-free days when the White method was applied, pine trees extracted nearly twice as much groundwater through ET g as the banksia, whereas no groundwater use by grasses was detected. Groundwater use is largely controlled by meteorological drivers but further mediated by depth to water table. The resulting annual net recharge (gross recharge minus ET g ) at the pine plantation was comparable to that of the banksia woodland but only half of the corresponding value at the grassland. Vegetation cover impacts potential groundwater recharge and discharge, but in these subtropical shallow water table environments estimates of potential recharge based on rainfall data need to take into account the often limited recharge capacity in the wet season.

A GIS Based Variable Source Area Model for Large-scale Basin Hydrology

A geographic information system-based rainfall runoff model that simulate variable source area runoff using topographic features of the basin is presented. The model simulate the flow processes on daily time step basis and has four non linear stores viz. Interception store, soil moisture store, channel store and ground water store. Source area fraction is modelled as a function of antecedent soil moisture, net rainfall and pore capacity raised to the power of areal average topographic index (Λ). Source area fraction is used in conjuction with topographic index to develop linear relations for runoff, Infiltration and interflow. An exponential relation is developed for lower zone evapotranspiration and non-linear exponential relations to model macropore flow and base flow are proposed.

Measuring and modeling rainfall interception losses by a native Banksia woodland and an exotic pine plantation in subtropical coastal Australia

Rainfall loss by canopy interception and subsequent evaporation to the atmosphere can be a significant portion of water loss from forested ecosystems. To quantify and compare interception losses from two forest types (exotic pine plantation vs. displaced native Banksia woodland) on Bribie Island in subtropical east coast Australia, we measured gross rainfall, throughfall and stemflow over a one-year period (May 2012–April 2013). Interception losses from both forests were also simulated by the revised Gash’s analytical model (RGAM) and the WiMo model. The results show that the annual interception loss in the Banksia woodland was lower (16.4% of gross rainfall) than that in the pine plantation (22.9% of gross rainfall) over the study period, which can be explained by the lower canopy storage capacity and higher aerodynamic resistance of the Banksia woodland. Using fixed parameters obtained from wet season (November–April), the optimized RGAM and WiMo models predict the interception losses from both forest stands reasonably well, with an underestimation of 8.5–12.7% for the dry season (May–October), and a total underestimation of 5.2–8.2% for the entire year. The results indicate the development of commercial pine plantations in these areas would result in an increase in interception losses and thus reduce the net rainfall input in these forested ecosystems.

Streamflow prediction in ungauged basins through geomorphology-based hydrograph transposition

Geomorphology-based rainfall–runoff models are particularly helpful for predicting hydrology in ungauged basins. The robustness, generality and flexibility of the modelling approach make it able to deal with a wide variety of processes, events and scales. It allows a rainfall–runoff transfer function to be estimated for any basin without needing to measure discharge. The aim of this study is to transpose hydrological observations from gauged to ungauged basins to predict streamflow hydrographs. It considers pairs of nested and neighbouring basins, the first one providing information for the second ungauged one. A time-series of the donor basin's discharge is deconvoluted by inverting its geomorphology-based transfer function to assess the time-series of net rainfall. The latter is then transposed to the receiver basin, where it is convoluted with the reciever basin's transfer function to predict the hydrograph therein. The methodology was implemented with virtual and real rainfall–runoff events on a set of basins in temperate Brittany, France. Different time scales and spatial configurations were tested. Goodness-of-fit of model predictions varied by basin pair. High prediction accuracy was observed when transposing hydrographs between nested basins differing greatly in size. Several ways to improve the approach are identified by relaxing simplifying assumptions.

The influence of the net rainfall mixed Curve Number – Green Ampt procedure in flood hazard mapping: a case study in Central Italy

A net rainfall estimation procedure, referred to as Curve-Number For Green-Ampt (CN4GA), combining the Soil Conservation Service - Curve Number (SCS-CN) method and the Green and Ampt (GA) infiltration equation was recently developed, aiming to distribute at subdaily time resolution the information provided by the SCS-CN method. The initial abstraction and the total volume of rainfall provided by the SCS-CN method are used to identify the ponding time and to quantify the hydraulic conductivity parameter of the GA equation, whereas the GA infiltration model distributes the total volume of the rainfall excess provided by the SCS-CN method. In this study we evaluate the proposed procedure with reference to a real case comparing the flood mapping obtained applying the event-based approach for two different net rainfall scenarios: the proposed CN4GA and the common SCS-CN. Results underline that the net rainfall estimation step can affect the final flood mapping result.

The influence of the net rainfall mixed Curve Number – Green Ampt procedure in flood hazard mapping: a case study in Central Italy

A net rainfall estimation procedure, referred to as Curve-Number For Green-Ampt (CN4GA), combining the Soil Conservation Service - Curve Number (SCS-CN) method and the Green and Ampt (GA) infiltration equation was recently developed, aiming to distribute at subdaily time resolution the information provided by the SCS-CN method. The initial abstraction and the total volume of rainfall provided by the SCS-CN method are used to identify the ponding time and to quantify the hydraulic conductivity parameter of the GA equation, whereas the GA infiltration model distributes the total volume of the rainfall excess provided by the SCS-CN method. In this study we evaluate the proposed procedure with reference to a real case comparing the flood mapping obtained applying the event-based approach for two different net rainfall scenarios: the proposed CN4GA and the common SCS-CN. Results underline that the net rainfall estimation step can affect the final flood mapping result.

Speleothem trace element signatures: A hydrologic geochemical study of modern cave dripwaters and farmed calcite

Trace element variations in ancient cave speleothems are often interpreted as indicators of changes in paleo-rainfall and hydrologic conditions. However, these records are difficult to interpret without an understanding of the physicochemical controls on stalagmite chemistry plus site-specific calibration of changes in net rainfall to variations in dripwater and speleothem chemistry. In this study we examine geochemical relationships between net rainfall (Precipitation minus Evapotranspiration; P−ET), drip rates, drip water chemistry, and contemporaneous calcite chemistry to test the hypothesis that speleothem Mg/Ca and Sr/Ca records are proxies for rainfall amount.HRC is contained within four low-magnesium limestone units capped sporadically by a remnant dolomitic limestone. Aqueous concentrations of magnesium (post evapotranspiration) decrease with increasing vertical travel distance between the soil zone and the point of in-cave drip emergence (Drip Path Length – DPL) as dissolved high-Mg solutions sourced from the dolomitic caprock are diluted with dissolved low-Mg limestone waters sourced from the host limestone. Dripwater Mg/Ca and Sr/Ca ratios covary and provide diagnostic indicators of the two dominant mechanisms controlling dripwater chemistry: (1) mixing of post-evaporative solutions derived from two geochemical endmembers (dissolution of dolomite and limestone); and (2) evolution of hydrochemistry away from dissolved bedrock compositions due to Prior Calcite Precipitation (PCP) above the drip sites. By resolving the linear mixing relationships for drip water Mg/Ca and Sr/Ca sources and the distribution coefficients for trace element transfer in the PCP dripwater-to-calcite precipitation reactions and applying these principles to our time series, we find that the extent of PCP production within the karst is directly controlled by the balance between Precipitation (P) and Evapotranspiration (ET): higher net rainfall (P−ET>1: wet conditions) reduces PCP, and lower net rainfall with increased evapotranspiration (P−ET<1) increases PCP.Farmed calcite X/Ca ratios faithfully track hydrologically-influenced seasonal variations in dripwater chemistry for X=Mg, Sr, and Na. However, the relationship between changes in net rainfall and changes in Mg/Ca and Sr/Ca ratios in modern calcite is unique at each site and differs significantly at closely-spaced drip/stalagmite locations. This suggests that in situ modern hydrochemical calibrations should be performed atop individual speleothems prior to harvesting for paleoclimate investigations, and that such calibrations may not reflect past conditions as drip paths change. We apply this understanding to published dripwater data and speleothem time series from other caves. A major implication is that in order to interpret stalagmite Sr/Ca and Mg/Ca ratios as ‘wet vs. dry’ proxies, speleothem Sr/Ca and Mg/Ca variations must be coherent and in-phase over all time periods (i.e., Sr/Mg ratios must be constant). These criteria will help to distinguish ‘rainfall amount’ versus ‘rainfall source’ in speleothem δ18O records.

SOME HYDROLOGICAL ASPECTS OF A NATURAL FOREST IN THE MID-COUNTRY INTERMEDIATE ZONE OF SRI LANKA

Total and net rainfall were measured by rain gauges in the open and under thecanopy, records front a station 5 kill aW(~y were also used. infiltration wasmeasured by a double ring infiltrometer. Transpiration was estimated frontchanges in soil-moisture storage, as measured by the neutron probe method.Provision lms made to measure surface runoff,' but there was none; injiltrationrates were well above maximum rainfall intensity. Although some of the data arenot complete, it is concluded that the tree vegetation loses relatively smallamount of water bv interception and transpiration in the dry season, for thereason that the roots have limited access to water.

Curve-Number/Green-Ampt Mixed Procedure for Net Rainfall Estimation: A Case Study of the Mignone Watershed, IT

A mixed procedure, referred to as CN4GA (Curve Number for Green-Ampt), was recently introduced with the aim of distributing in time the net rainfall volume provided at event scale by the Soil Conservation Service - Curve Number (SCS-CN) method. The proposed method consists in employing the Green-Ampt infiltration equation and calibrating both the ponding time and the soil hydraulic conductivity using the initial abstraction and the total volume given by the SCS-CN method. The procedure is here applied on several rainfall-runoff events observed in an Italian watershed. Results confirms the general behavior already noticed in previous studies: the CN4GA procedure provides net rainfal intensities consistent with the runoff observations, the SCS-CN method underestimates peak intensity when applied at sub-daily* resolution, and the differences between the two approaches are relevant when the gross rainfall peak occurs at the beginning of the storm and generally in case of multi-peak events.

A Preliminary Study on Rainfall Interception Loss and Water Yield Analysis on Arabica Coffee Plants in Central Aceh Regency, Indonesia

Abstract - Rainfall interception loss from plants or trees can reduce a net rainfall as source of water yield. The amount of rainfall interception loss depends on kinds of plants and hydro-meteorological characteristics. Therefore, it is important to study rainfall interception loss such as from Arabica Coffee plantation which is as main agricultural commodity for Central Aceh Regency. In this study, rainfall interception loss from Arabica Coffee plants was studied in Kebet Village of Central Aceh Regency, Indonesia from January 20 to March 9, 2011. Arabica coffee plants used in this study was 15 years old, height of 1.5 m and canopy of 4.567 m2. Rainfall interception loss was determined based on water balance approach of daily rainfall, throughfall, and stemflow data. Empirical regression equation between rainfall interception loss and rainfall were adopted as a model to estimate rainfall interception loss from Arabica Coffee plantation, which the coefficient of correlation, r is 0.98. In water yield analysis, this formula was applied and founded that Arabica Coffee plants intercept 76% of annual rainfall or it leaved over annual net rainfall 24% of annual rainfall. Using this net rainfall, water yield produced from Paya Bener River which is the catchment area covered by Arabica Coffee plantation was analyzed in a planning of water supply project for water needs domestic of 3 sub-districts in Central Aceh Regency. Based on increasing population until year of 2025, the results showed that the water yield will be not enough from year of 2015. However, if the catchment area is covered by forest, the water yield is still enough until year of 2025

A software-based sensor for combined sewer overflows

A new methodology for online estimation of excess flow from combined sewer overflow (CSO) structures based on simulation models is presented. If sufficient flow and water level data from the sewer system is available, no rainfall data are needed to run the model. An inverse rainfall-runoff model was developed to simulate net rainfall based on flow and water level data. Excess flow at all CSO structures in a catchment can then be simulated with a rainfall-runoff model. The method is applied to a case study and results show that the inverse rainfall-runoff model can be used instead of missing rain gauges. Online operation is ensured by software providing an interface to the SCADA-system of the operator and controlling the model. A water quality model could be included to simulate also pollutant concentrations in the excess flow.

Embedding isochronous cells overland flow module into MODFLOW

AbstractThis study integrates a simple overland flow module (isochronous cells model) with the river module of MODFLOW such that temporal and spatial interactions between stream flow and groundwater can be simulated using net rainfall data of a watershed. The isochronous cells model is an efficient travel time runoff approach based on geographic information system (GIS) that considers both spatial and temporal variations of net rainfall through hill slope of the watershed. This overland module is easily coupled with MODFLOW river routing module. Specifically, the stream flow from the isochronous cells model is directly assigned to both sides of river cells of the MODFLOW model. Such an integration of MODFLOW and isochronous cells model is especially useful in watersheds where river flow data are limited. The feasibility of this integrated model was demonstrated using a case study in the middle and downstream regions of the Yitong River watershed, China. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Green‐Ampt Curve‐Number mixed procedure as an empirical tool for rainfall–runoff modelling in small and ungauged basins

AbstractThe Soil Conservation Service Curve Number (SCS‐CN) method is a popular rainfall–runoff model that is widely used to estimate direct runoff from small and ungauged basins. The SCS‐CN is a simple and valuable approach to quantify the total streamflow volume generated by storm rainfall, but its use is not appropriate for estimating the sub‐daily incremental rainfall excess. To overcome this drawback, we propose to include the Green‐Ampt (GA) infiltration model into a mixed procedure, which is referred to as Curve Number for Green‐Ampt (CN4GA), aiming to distribute in time the information provided by the SCS‐CN method. For a given storm, the computed SCS‐CN total net rainfall amount is employed to calibrate the soil hydraulic conductivity parameter of the GA model. The proposed procedure is evaluated by analysing 100 rainfall–runoff events that were observed in four small catchments of varying size. CN4GA appears to provide encouraging results for predicting the net rainfall peak and duration values and has shown, at least for the test cases considered in this study, better agreement with the observed hydrographs than the classic SCS‐CN method. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Historical rainfall-runoff modeling of river Ogunpa, Ibadan, Nigeria

Flooding in major cities like the city of Ibadan, the largest urban centre south of the Sahara, Africa, is a common phenomena. Flooding occurred in several areas of the city each time when Ogunpa River overflowed its banks. Flood damage mitigation measures were necessitated by increased runoff due to rapid urbanization of the catchment area coupled with inadequate runoff data along the river course. Ogunpa River gained its national and international notoriety when many lives and properties worth billions of Naira were lost in the floods of 1960, 1963, 1978, 1980 and 2011. This study was conducted at Queen Elizabeth gauging station to develop an historical rainfall-runoff model for River Ogunpa. The model developed was a linear regression approach considering the effects of previous and current rainfall on the flow of the effluent streams. Average daily net rainfall data and average daily rainfall were regressed against average daily runoff data. Using linear regression method Net rainfall values (R') and rainfall values (R) were regressed against the corresponding discharge (Q) arrived at correlation coefficients of 0.66975 and 0.71191989 respectively. Utilizing 101 years of rainfall records for Ibadan City, runoff data for Ogunpa River were derived. This data could serve as a veritable hydrologic input in the design of embankment flood mitigation structures for River Ogunpa. It is recommended that to find a lasting solution to the menacing frequent flooding more runoff gauging stations be provided along the river course of Ogunpa River within Ibadan metropolis.

IMPACT OF LAND USE CONVERSIONS ON WATER YIELD

Trees use more water than shorter vegetation due to comparatively high interception and evaporation losses. These losses also vary with the different tree species and climatic conditions. In high elevations, trees could offset the interception losses by capturing horizontally driven fog into the catchment system. Therefore, it is important to study the hydrological processes which would help to estimate water use of different land cover types which in turn is required to find the effect of land use conservation on water yield.Only two studies with limited duration have been carried out to find the effect of land cover on a few hydrological processes in 1977 and 1988. Therefore, a long-term research project has been carried out since 1993 at two sites, namely at Dodangolla and Horton plains, to monitor the hydrological processes in detail under different land use types. Home gardens, grass and Acacia are being selected at the low elevation site, while montane forests, grassland and Pinus are being selected for the high elevation site.These two sites are instrumented with automatic weather stations which monitor rainfall at 5 minutes intervals and other climatological parameters at hourly intervals. Net rainfall gauges with tipping buckets are installed to measure interception. Soil moisture is being monitored with access tubes and neutron probes at the two sites. A fog collector is installed at the Horton plain site to measure the horizontally driven fog at hourly intervals.The results from this study will be used to calibrate a water use model for different land use types. Once this is accomplished, the model can be used to predict the effect of land use conservation on water yield.

Quantification of urbanization impacts on discharge volume using H2U model

Urbanization tends to change in peak discharge and runoff volumes of natural catchments. In this study, the results of H2U model with the production function used for net rainfall calculation were compared to observed hydrographs. In the production function, mapped impervious area (MIA) and effective impervious area (EIA) values were tested for imperviousness parameter. A test catchment located in Tehran City was selected for this purpose whereas; part of this area was considered to compare pre and post developed conditions. Performance indicators verified that urban catchment hydrographs most closely resembled the observed hydrographs when using effective impervious area value in the production function. The comparison of pre and post development hydrographs in part of the catchment revealed urbanization leads to 95% increase in peak discharge rate and 50% decrease in unit hydrograph time base. The post developed condition runoff volume of 10 year return period rainfall event was 4.01 times more than pre developed runoff volume originated from decreasing hydraulic length and increasing impervious areas. Moreover; the results of this study revealed that the effect of Strahler order drainage network change on peak discharge rate was greater than decrease of hydraulic length. Key words: Effective impervious area, morphological approach, net rainfall, urbanization.

Final Scientific Report: 'Processing and Hydrogeological Analysis of the Data of the November 2003 Flood Event in the Reno River Closed at Pracchia'

An interesting case study for the implementation of the model was identified by the DISTART research group in the Northern Apennine Mountains, as requested by the LAMPIT research group. The identified watershed is the most upstream part of Reno river basin, at the closure section of Pracchia, located in the Tuscan part of the Reno watershed, close to the border with the Regione Emilia Romagna. Following an analysis of the rainfall and stream flow data collected from 2002 and 2007, the flood event that took place at the beginning of November 2003 (days 7-9) was identified as one of the most severe meteorological events in the whole observation period. The rainfall event was characterized by high rainfall intensities for several hours over the entire northern Apennine area and it corresponded to a significant flood hydrograph at the Pracchia cross-section. As required by the LAMPIT and CIRA, the following data, needed for the implementation of both hydrological/hydraulic and meteorological modelling, were collected, processed and delivered to either the CIRA or the LAMPIT research groups by the end of July 2009. In addition to the collection and processing of the above data, the DISTART group performed the research activities needed for issuing the following products (delivered to the LAMPIT research group on the 30th September 2009): the spatially distributed hourly rainfall fields on the basis of the ground raingauge data, for each hour from 0.00, 7 November 2003 to 23.00, 9 November 2003, that is the total (or gross) hourly rainfall fields (in a matrix form, following the standards required by the LAMPIT research group, that is for cells of 20 m x 20 m) over the watershed area; an estimate of the spatio-temporal distribution of the net rainfall, that is of the part of the gross rainfall that actually becomes surface runoff (or overland flow). Net rainfall is obtained is subtracting from the gross rainfall the water losses ascribed to: interception by the vegetation, depression storage (or surface retention) and infiltration. A net rainfall map, over the watershed (plus buffer) area, was computed for each hour from 0.00, 7 November 2003 to 23.00, 9 November 2003.