Initial Soil Moisture Content Research Articles

Copula-based interpretation of continuous rainfall–runoff simulations of a watershed in northern Iran

In the present work, the joint response of key hydrologic variables, including total precipitation depths and the corresponding simulated peak discharges, are investigated for different antecedent soil moisture conditions using the copula method. The procedure started with the calibration and validation of the soil moisture accounting (SMA) loss rate algorithm incorporated in the Hydrologic Engineering Center – hydrologic modeling system (HEC–HMS) model for the study watershed. A 1000 year long time series of hourly rainfall was then generated by the Neyman–Scott rectangular pulses (NSRP) rainfall generator, which was then transformed into the runoff rate by the HEC–HMS model. This long-term continuous hydrological simulation resulted in characterizing the response of the watershed for various input conditions such as initial soil moisture content (AMC), total rainfall depth, and rainfall duration. For each initial soil moisture class, the copula method was employed to determine the joint probability distribution of rainfall depth and peak discharge. For instance, for dry AMC condition and 1 h rainfall duration, the Joe family fitted best to the data, compared with six other one-parameter families of copulas. Results showed that the bivariate analysis of rainfall–runoff using the copula method can well characterize the watershed hydrological behavior. The derived offline curves could provide a probabilistic real-time peak discharge forecast.

Initial Soil Water Content as Input to Field-Scale Infiltration and Surface Runoff Models

Evidence is given of the role of initial soil moisture content, θi, in determining the surface runoff hydrograph at field scale, that is a crucial element when distributed models for the estimate of basin response to rainfall have to be formulated. This analysis relies upon simulations performed by a model that, because of the necessity of representing the infiltration of surface water running downslope into pervious saturated or unsaturated areas, uses a coupled solution of a semi-analytical/conceptual approach for local infiltration and a nonlinear kinematic wave equation for overland flow. The model was applied to actual spatial distributions of θi, earlier observed over different fields, as well as to a uniform value of θi assumed equal to the average value or to the value observed in a site characterized by temporal stability. Our results indicate that the surface runoff hydrograph at a slope outlet is characterized by a low sensitivity to the horizontal heterogeneity of θi, at least in the cases of practical hydrological interest. In fact, in these cases the correct hydrograph can be simulated with considerable accuracy replacing the actual distribution of θi by the corresponding average value. Moreover, the surface hydrograph is sufficiently well reproduced even though a single value of θi, observed at a site anyhow selected in the field of interest, is used. In particular, this extreme simplification leads to errors in magnitude on peak runoff and total volume of surface water with values typically within 10% and 15%, respectively.

Impact of ASAR soil moisture data on the MM5 precipitation forecast for the Tanaro flood event of April 2009

Abstract. The representation of land-atmosphere interactions in weather forecast models has a strong impact on the Planetary Boundary Layer (PBL) and, in turn, on the forecast. Soil moisture is one of the key variables in land surface modelling, and an inadequate initial soil moisture field can introduce major biases in the surface heat and moisture fluxes and have a long-lasting effect on the model behaviour. Detecting the variability of soil characteristics at small scales is particularly important in mesoscale models because of the continued increase of their spatial resolution. In this paper, the high resolution soil moisture field derived from ENVISAT/ASAR observations is used to derive the soil moisture initial condition for the MM5 simulation of the Tanaro flood event of April 2009. The ASAR-derived soil moisture field shows significantly drier conditions compared to the ECMWF analysis. The impact of soil moisture on the forecast has been evaluated in terms of predicted precipitation and rain gauge data available for this event have been used as ground truth. The use of the drier, highly resolved soil moisture content (SMC) shows a significant impact on the precipitation forecast, particularly evident during the early phase of the event. The timing of the onset of the precipitation, as well as the intensity of rainfall and the location of rain/no rain areas, are better predicted. The overall accuracy of the forecast using ASAR SMC data is significantly increased during the first 30 h of simulation. The impact of initial SMC on the precipitation has been related to the change in the water vapour field in the PBL prior to the onset of the precipitation, due to surface evaporation. This study represents a first attempt to establish whether high resolution SAR-based SMC data might be useful for operational use, in anticipation of the launch of the Sentinel-1 satellite.

Factors affecting GCL hydration under isothermal conditions

The hydration of different GCLs from the pore water of the underlying foundation soil is investigated for isothermal conditions at room temperature. Results are reported for three different reinforced (needle punched) GCL products. Both a silty sand (SM) and sand (SP) foundation soil are examined. GCL hydration is shown to be highly dependant on the initial moisture content of the foundation soil. GCLs on a foundation soil with a moisture content close to field capacity hydrated to a moisture content essentially the same as if immersed in water while those on soil at an initial moisture content close to residual only hydrated to a gravimetric moisture content of 30–35%. The method of GCL manufacture is shown to have an effect on the rate of hydration and the final moisture content. The presence or absence of a small (2 kPa) seating pressure is shown to affect the rate of hydration but not the final moisture content. The GCL hydration did not change significantly irrespective of whether a nonwoven cover or woven carrier GCL rested on the foundation soil.

Numerical Simulation and Analysis on the Heat Transfer of the Vertical Ground Heat Exchanger in Hydrous Soil

Based on the law of mass and energy conservation and the one-dimensional model of heat transfer, a heat and moisture transfer line source model for the ground-source heat pump system has been developed. Numerical simulation results in summer working conditioning indicate that the affect of moisture transfer in soil was mainly around the U-type tube. When the soil moisture content is high, the capacity of heat transfer in soil is good. The heat transfer capacity of the ground heat exchanger calculated by the model in this work is lower than those which are calculated by the common heat transfer model. When the initial soil moisture content is about 0.1, the difference calculated by the two model is about 18%.

Performance of infiltration swales with regard to operation in winter times in an Alpine region

In cold climate regions winter conditions significantly influence the performance of stormwater infiltration devices. Frozen soil and water storage by snow changes their operation. In this paper winter operation of a grassed infiltration swale was investigated using on-site and laboratory measurements. The field investigation of a grassed swale at a parking place in an Alpine region showed that the swale fulfilled its function properly. Although the top layer was frozen for some time, the storage capacity of the swale was sufficient to store the precipitation until the conditions improved. The soil attenuated the air temperature, at 20 cm below ground surface the soil was only frozen for one week. winter maintenance proved to be a problem, together with the snow from the parking place a lot of gravel and fine particles were deposited at one end of the swale. This decreased the hydraulic conductivity at that point significantly. The laboratory tests with soil columns showed an increase of flow time through the soil column with decreasing soil moisture content. For soil temperatures below 0 degrees C the hydraulic conductivity was reduced for increasing initial soil moisture contents. All in all the hydraulic conductivity was best around 0 degrees C for all soil water contents. However, also at minus 5 degrees C the coefficient of hydraulic conductivity was always at least above 10(-6) m/s, thus within the range of tolerated hydraulic conductivity specified in the national guidelines. Nevertheless, the handling of the soil was found to have high influence on the results. The results indicate that in the Alpine region infiltration swales operate sufficiently under winter conditions although with decreased performance.

A laboratory experimental study of high-temperature thermal storage in the unsaturated soil using a vertical borehole heat exchanger

High-temperature thermal storage (HTTS) in soils is a promising energy-saving technology for space heating of buildings. Based on a laboratory experimental setup using a vertical borehole heat exchanger (BHE), dynamic changes of the soil temperature and moisture content during the thermal storage process are studied. Effects of the heat injection temperature and initial moisture content on the thermal performance of the BHE are analyzed. The results show that at the first thermal storage stage, the soil temperature and moisture content near the heat source may appear a temporary peak. Its occurrence depends on the initial soil moisture content, the heat injection temperature and the distance from the heat source. As the heat injection temperature increases, the heat transfer rate of the BHE increases greatly. As the initial soil moisture content increases, the temperature profile near the BHE tends to be deviated from the results predicted by heat conduction, thereby influencing the thermal performance of the BHE. The present results can provide useful guidelines for the design of an HTTS system. Copyright , Oxford University Press.

Small Catchment Agricultural Management Using Decision Variables Defined at Catchment Scale and a Fuzzy Rule-Based System: A Mediterranean Vineyard Case Study

Physically based hydrological models are increasingly used to simulate the impact of land use changes on water and mass transfers. The problems associated with this type of parameter-rich model from a water management perspective are related to the need for (1) a large number of local parameters instead of only a few catchment-scale decision variables and (2) the technical skills and computational expertise necessary to perform these models. This study aimed to show that it is possible to define a reduced number of decision variables and rules to synthesise numerical simulations carried out through a physically based model. The MHYDAS model was run on a Mediterranean vineyard catchment located in southern France (Roujan, Herault) for an actual, common rainfall event to calculate the runoff coefficient. The simulation results concerned 3,000 samples of contrasted scenarios. The scenarios were characterised by four catchment-scale decision variables related to agricultural practices: the proportion of the area of non agricultural land, the proportion of the area subjected to full chemical weeding practices (with the complement being mechanical weeding), the spatial arrangement of the practices based on the distance to the outlet and the initial soil moisture content. The simulation results were used to generate fuzzy linguistic rules to predict the runoff coefficient, as computed by the physical model from the decision variables. For a common end of spring rainfall event, simulations showed that the runoff coefficient was most heavily influenced by the initial soil moisture and the proportion of the area of full chemical weeding practices and the proportion of the area of other land uses and their spatial arrangement also played a role. The fuzzy rule-based model was able to reproduce the hydrological output with good accuracy (R2 = 0.97). Sensitivity analysis to the rainfall magnitude showed that if the amount of rainfall was the key factor explaining the runoff coefficient absolute values, the structure of the rule base remained stable for rainfall events close to the one studied.

Dual state-parameter estimation of root zone soil moisture by optimal parameter estimation and extended Kalman filter data assimilation

With well-determined hydraulic parameters in a hydrologic model, a traditional data assimilation method (such as the Kalman filter and its extensions) can be used to retrieve root zone soil moisture under uncertain initial state variables (e.g., initial soil moisture content) and good simulated results can be achieved. However, when the key soil hydraulic parameters are incorrect, the error is non-Gaussian, as the Kalman filter will produce a persistent bias in its predictions. In this paper, we propose a method coupling optimal parameters and extended Kalman filter data assimilation (OP-EKF) by combining optimal parameter estimation, the extended Kalman filter (EKF) assimilation method, a particle swarm optimization (PSO) algorithm, and Richards’ equation. We examine the accuracy of estimating root zone soil moisture through the optimal parameters and extended Kalman filter data assimilation method by using observed in situ data at the Meiling experimental station, China. Results indicate that merely using EKF for assimilating surface soil moisture content to obtain soil moisture content in the root zone will produce a persistent bias between simulated and observed values. Using the OP-EKF assimilation method, estimates were clearly improved. If the soil profile is heterogeneous, soil moisture retrieval is accurate in the 0–50 cm soil profile and is inaccurate at 100 cm depth. Results indicate that the method is useful for retrieving root zone soil moisture over large areas and long timescales even when available soil moisture data are limited to the surface layer, and soil moisture content are uncertain and soil hydraulic parameters are incorrect.

VAKUM VE SERBEST ATMOSFER ŞARTLARI ALTINDA HAVADA KURU TOPRAK NUMUNESİNİ SUYA BATIRARAK ISLATMA SONUNDA ELDE EDİLEN SUYA MUKAVİM AGREGAT ÖLÇMELERİ ÜZERİNE BAŞLANGıÇ RUTUBET MUHTEVASININ TESİRLERİNİN TESBİTİ ÜZERİNDE BİR ARAŞTIRMA

OZET Bu calisma, struktur tayininde islak-eleme ameliyesinden once, havada kuru toprak numunesini suya batirarak islatma sartlari altinda agregat parcalanmasina sebep olan kuuvvetlerin ki hapsedilmis hava ve suyun dispers etme hareketinin nasil calistiigini tetkik gayesiyle yapilmistir. Iskocya-Aberdin dolaylarindan ince kumJu-killi-tinli bir teksture sahip bir tarla topraginin ust 0-20 cm'Jik tabakasindan alinan toprak numunesi uzerinde asagidaki husus/ar bulunmu.;tur : 1) Havada kuru toprak rutubeti azalirken, hapsedilmis havanin agregat/ar uzerine parcalayici etkisi artmaktadir. 2) Bu etki, agregat buyuklugu 1 mm'nin uzerinde artarken artmistir. 3) Gerek vakum ve gerekse serbest atmosfer sart/an altinda suya batirarak is/atildigi zaman, baslangic havada kuru toprak rutubet muhtevasi artarken suya-mukavim agregat miktarlan da artmaktadir. SUMMARY Study on the Elfeet of Iniiial Soit Moisture Contetit on the WaterStable Aggregates obtained on Re-Wetting by Immersion under Vaeuum and Non- Vaeuum Conditions. This work was intended to find out how the components of aggregate breakdown due to entrapped air and the dispersing action of water work on r-e-wetting by immersion before wet-sieving. It was carried out on a soil sample of fine sandy-Ciay-loam textured and taken from the tdp 0-20 cm. layer of a field, been under grass for about 25 years, at Cruden Bay around Aberdeen, Scotland. After airdrying and screening through a 3 mm. mesh sieve, the sample was re-wetted by immersion under both vacuum and non-vacuum conditions at two levels of initiaI soil moisture content before- wet-sjeving by the method developed by Williamson et all. (1956). it was found that I) When the initial soil mOlJsture decreased, the disrupting etTect of entrapped air increased. 2) This effect was more pronounced as the aggregate size increased above i mm. in diameter. 3) Under both vacuum and nonvacuum conclitions, when the initial soil moisture content increased, the water-suible aggregates increased, when re-wetted by immersion.

Using a H∞ filter assimilation procedure to estimate root zone soil water content

AbstractRoot zone soil water content impacts plant water availability, land energy and water balances. Because of unknown hydrological model error, observation errors and the statistical characteristics of the errors, the widely used Kalman filter (KF) and its extensions are challenged to retrieve the root zone soil water content using the surface soil water content. If the soil hydraulic parameters are poorly estimated, the KF and its extensions fail to accurately estimate the root zone soil water. The H‐infinity filter (HF) represents a robust version of the KF. The HF is widely used in data assimilation and is superior to the KF, especially when the performance of the model is not well understood. The objective of this study is to study the impact of uncertain soil hydraulic parameters, initial soil moisture content and observation period on the ability of HF assimilation to predict in situ soil water content. In this article, we study seven cases. The results show that the soil hydraulic parameters hold a critical role in the course of assimilation. When the soil hydraulic parameters are poorly estimated, an accurate estimation of root soil water content cannot be retrieved by the HF assimilation approach. When the estimated soil hydraulic parameters are similar to actual values, the soil water content at various depths can be accurately retrieved by the HF assimilation. The HF assimilation is not very sensitive to the initial soil water content, and the impact of the initial soil water content on the assimilation scheme can be eliminated after about 5–7 days. The observation interval is important for soil water profile distribution retrieval with the HF, and the shorter the observation interval, the shorter the time required to achieve actual soil water content. However, the retrieval results are not very accurate at a depth of 100 cm. Also it is complex to determine the weighting coefficient and the error attenuation parameter in the HF assimilation. In this article, the trial‐and‐error method was used to determine the weighting coefficient and the error attenuation parameter. After the first establishment of limited range of the parameters, ‘the best parameter set’ was selected from the range of values. For the soil conditions investigated, the HF assimilation results are better than the open‐loop results. Copyright © 2010 John Wiley & Sons, Ltd.

Potential urea-derived nitrogen losses caused by ammonia volatilization and nitrogen leaching in a rainfed semiarid region, China

In the rainfed semiarid region of the China Loess Plateau, rainfall is concentrated in the growing season and usually occurs in large storms. This makes for a high risk for fertilizer-derived nitrogen losses. However, relatively little attention has been given to fertilizer efficiency in this region. In this study, ammonia volatilization at natural field conditions as affected by urea-application rate was measured to evaluate the potential ammonia volatilization losses. Nitrogen-leaching potential in the 0–100 cm soil profile as affected by urea-application rate and -application depth for different rainfall-simulated irrigation regimes (two irrigation volumes: 70 and 105 mm; two irrigation methods: single irrigation and three-split irrigation) was also investigated. Results showed that the low initial soil moisture content at the crop-planting stage and a strong following rainfall made ammonia volatilization of low importance from an agricultural management perspective. The stock percentage of urea-derived nitrogen in the soil profile was significantly affected by irrigation method and irrigation volume but not by urea-application rate. Generally, the 105 mm irrigation volume and the single-irrigation method had a lower percentage of applied nitrogen remaining in the soil profile. The results of this rainfall-simulated irrigation investigation indicated that heavy rainfall, especially occurring in large storms, in this area increased the risk of nitrogen leaching. We recommend that split applications of urea should be adopted instead of a conventional lumped (single) application to reduce nitrogen losses in this rainfed semiarid region.

Summertime land‐atmosphere interactions in response to anomalous springtime snow cover in northern Eurasia

An atmospheric general circulation model (AGCM) is used to investigate the effects of springtime high‐latitude snow cover on the summertime climate system in the form of land‐atmosphere interactions in northern Eurasia. We performed light and heavy snow runs in which the initial snow mass in northern Eurasia was varied. Significant differences in model response between the light and heavy snow runs are evident in terms of not only land surface parameters but also summertime northern atmospheric circulation. Changes in the initial snow cover have a strong effect on the simulated surface air temperature. In western Siberia, the albedo of the snow cover makes a strong contribution to the difference in surface heating between the runs, because snow mass anomalies are still present over western Siberia in June. In eastern Siberia (the Lena Basin), where the snow disappears in June in both runs, the snow‐hydrological effect is prominent throughout summer. The increased soil moisture in the heavy snow run causes increased evaporation, resulting in turn in surface cooling. The initial soil moisture content is dry in eastern Siberia and wet in western Siberia, resulting in contrasting responses between the two regions. In the light snow run, the subpolar jet is strengthened and maintained along the Arctic coast in early summer, and wave activity propagates eastward over northern Eurasia. Changes in the atmospheric circulation generate an east‐west dipole structure of precipitation anomalies over northern Eurasia. These results suggest that variations in the springtime Eurasian snow mass result in changes in the summertime northern atmospheric circulation and hydrological cycle via land‐atmosphere interactions.

Sensitivity of LISEM predicted catchment discharge to initial soil moisture content of soil profile

This study conducts a broad sensitivity analysis, taking into account the influence of initial soil moisture content in two soil layers, layer depths, event properties, and two infiltration models. A distributed hydrology and soil erosion model (LISEM) is used. Using the terrain data from the Catsop research catchment and two different rainfall events, the sensitivity of discharge is investigated for a range of pre-event soil moisture contents (0.1-0.40 cm(3) cm(-3)) in two-layers for a two-layer Green-Ampt as well as Richards infiltration model. The sensitivity of the predicted discharge to the initial condition of soil moisture appears to depend highly on all factors: infiltration model, event properties, topsoil/subsoil depth configuration and the level of the initial condition itself. There are interaction effects between all the factors. However, the effect of the different infiltration models is most pronounced. The Green-Ampt model shows less sensitivity to moisture content variation of both top and subsoil. Top/subsoil depth configuration rarely influences the results of the Green-Ampt model. The Richards model shows a highly variable discharge - initial soil moisture relation with changing rainfall intensity and topsoil/subsoil depth configurations. Two methods of sensitivity analysis, relative sensitivity and One factor-At-a Time sensitivity, have been used. The two methods gave comparable results. Depending on the other parameter values, 1% changes in topsoil moisture content resulted into 0.8-1.81% and 0.03-3.5% changes in total discharge predicted by the Green-Ampt and Richards models, respectively.

Martian base agriculture: The effect of low gravity on water flow, nutrient cycles, and microbial biomass dynamics

The latest advances in bioregenerative strategies for long-term life support in extraterrestrial outposts such as on Mars have indicated soil-based cropping as an effective approach for waste decomposition, carbon sequestration, oxygen production, and water biofiltration as compared to hydroponics and aeroponics cropping. However, it is still unknown if cropping using soil systems could be sustainable in a Martian greenhouse under a gravity of 0.38 g. The most challenging aspects are linked to the gravity-induced soil water flow; because water is crucial in driving nutrient and oxygen transport in both liquid and gaseous phases, a gravitational acceleration lower than g = 9.806 m s −2 could lead to suffocation of microorganisms and roots, with concomitant emissions of toxic gases. The effect of Martian gravity on soil processes was investigated using a highly mechanistic model previously tested for terrestrial crops that couples soil hydraulics and nutrient biogeochemistry. Net leaching of NO 3 - solute, gaseous fluxes of NH 3, CO 2, N 2O, NO and N 2, depth concentrations of O 2, CO 2 and dissolved organic carbon (DOC), and pH in the root zone were calculated for a bioregenerative cropping unit under gravitational acceleration of Earth and for its homologous on Mars, but under 0.38 g. The two cropping units were treated with the same fertilizer type and rate, and with the same irrigation regime, but under different initial soil moisture content. Martian gravity reduced water and solute leaching by about 90% compared to Earth. This higher water holding capacity in soil under Martian gravity led to moisture content and nutrient concentrations that favoured the metabolism of various microbial functional groups, whose density increased by 5–10% on Mars as compared to Earth. Denitrification rates became substantially more important than on Earth and ultimately resulted in 60%, 200% and 1200% higher emissions of NO, N 2O and N 2 gases, respectively. Similarly, O 2 and DOC were consumed more rapidly in the Martian soil and resulted in about 10% increase in CO 2 emissions. More generally, Martian cropping would require 90% less water for irrigation than on Earth, being therefore favourable for water recycling treatment; in addition, a substantially lower nutrient supply from external sources such as fertilizers would not compromise nutrient delivery to soil microorganisms, but would reduce the large N gas emissions observed in this study.

Effects of changing climate on water and nitrogen availability with implications on the productivity of Norway spruce stands in Southern Finland

An integrated process-based model was used to study how the changing climate affects the availability of water and nitrogen, and consequently the dynamics of productivity of Norway spruce ( Picea abies) on sites with different initial soil water conditions in southern Finland over a 100-year period. The sensitivity of the total stem volume growth in relation to short-term availability of water and nitrogen was also analyzed. We found that a high proportion (about 88–92%) of the total precipitation was lost in total evapotranspiration (incl. canopy evaporation ( E c), transpiration ( E t) and ground surface evaporation ( E g)), under both current and changing climate. Furthermore, under the changing climate the cumulative amount of E c and E g were significantly higher, while E t was largely lower than under the current climate. Additionally, the elevated temperature and increased expansion of needle area index ( L) enhanced E c. Under the changing climate, the increasing soil water deficit ( W d) reduced the canopy stomatal conductance ( g cs), the E t, humus yield ( H, available nitrogen source) and nitrogen uptake ( N up) of the trees. During the latter phases of the simulation period, the canopy net photosynthesis ( P nc) was lower due to the reduced N up and soil water availability. This also reduced the total stem volume production ( V s) on the site with the lower initial soil moisture content. The growth was slightly more sensitive to the change in precipitation than to the change in nitrogen content of the needles, when the elevated temperature was assumed. According to our findings, drought stress episodes may become more frequent under the changing climate. Thus, adaptive management strategies should be developed to sustain the productivity of Norway spruce in these conditions, and thus, to mitigate the adverse impacts of climate change.

Linking hydraulic properties of fire-affected soils to infiltration and water repellency

Summary Heat from wildfires can produce a two-layer system composed of extremely dry soil covered by a layer of ash, which when subjected to rainfall, may produce extreme floods. To understand the soil physics controlling runoff for these initial conditions, we used a small, portable disk infiltrometer to measure two hydraulic properties: (1) near-saturated hydraulic conductivity, K f and (2) sorptivity, S ( θ i ), as a function of initial soil moisture content, θ i , ranging from extremely dry conditions ( θ i 3 cm −3 ) to near saturation. In the field and in the laboratory replicate measurements were made of ash, reference soils, soils unaffected by fire, and fire-affected soils. Each has a different degrees of water repellency that influences K f and S ( θ i ). Values of K f ranged from 4.5 × 10 −3 to 53 × 10 −3 cm s −1 for ash; from 0.93 × 10 −3 to 130 × 10 −3 cm s −1 for reference soils; and from 0.86 × 10 −3 to 3.0 × 10 −3 cm s −1 , for soil unaffected by fire, which had the lowest values of K f . Measurements indicated that S ( θ i ) could be represented by an empirical non-linear function of θ i with a sorptivity maximum of 0.18–0.20 cm s −0.5 , between 0.03 and 0.08 cm 3 cm −3 . This functional form differs from the monotonically decreasing non-linear functions often used to represent S ( θ i ) for rainfall–runoff modeling. The sorptivity maximum may represent the combined effects of gravity, capillarity, and adsorption in a transitional domain corresponding to extremely dry soil, and moreover, it may explain the observed non-linear behavior, and the critical soil-moisture threshold of water repellent soils. Laboratory measurements of K f and S ( θ i ) are the first for ash and fire-affected soil, but additional measurements are needed of these hydraulic properties for in situ fire-affected soils. They provide insight into water repellency behavior and infiltration under extremely dry conditions. Most importantly, they indicate how existing rainfall–runoff models can be modified to accommodate a possible two-layer system in extremely dry conditions. These modified models can be used to predict floods from burned watersheds under these initial conditions.

Validation of soil moisture simulations from the PAMII model, and an assessment of their sensitivity to uncertainties in soil hydraulic parameters

Soil moisture simulations by the Canadian prairie agrometeorological model (PAMII) were validated against in situ observations from three sites on the Canadian prairies. Skill scores indicate that PAMII shows significant skill in simulating the evolution of bulk root-zone soil moisture content during the growing season, and that PAMII also captures the salient features of the soil moisture at each site. Specifically, correlation coefficients between simulated and observed bulk root-zone soil moisture content varied between 0.65 and 0.90, while the relative mean absolute errors were typically less than 10%. We adopted an ensemble approach to quantify the uncertainty in simulating soil moisture that results from errors in the soil hydraulic properties. The ensemble was assembled by running PAMII using soil hydraulic properties from 20 pedotransfer functions (PTFs). Our results suggests that the uncertainty in soil moisture estimates is typically less than 10% of the bulk root-zone soil moisture content, and that there appears to be merit in using a PTF ensemble to improve estimates of the soil's hydraulic properties. In addition, the simulated soil moisture was quite sensitive to the reference stomatal resistance term. For the grassland sites, a reference value of 100 s m −1 yielded the best results. The accuracy of the soil moisture simulations was insensitive to errors <5% in the initial plant-available soil moisture content. The skill of PAMII is strongly modulated by errors in the estimated permanent wilting point and field capacity, with the skill of model simulations typically increasing as the errors decrease. Consequently, the correct modelling of soil moisture is contingent on accurately specifying the site-specific soil hydraulic properties.

Modelling the impact of urbanisation on flood runoff volume

In this study, a relatively simple and intuitive extension to an event-based lumped conceptual rainfall–runoff model, the revitalised flood hydrograph model is introduced and shown to improve model performance on a heavily urbanised catchment. The extension does not affect model performance on a rural catchment. The hydrological losses in the model are calculated based on a percentage runoff type model, initially developed for use in rural catchments and relating losses to soil moisture content, soil moisture capacity and rainfall. By assuming a fixed percentage runoff of 70% from the urban (impervious) parts of the catchment, an overall improvement in predictive ability of the extended urban model is observed on the heavily urbanised catchment. Model performance is generally found to be improved more when considering events occurring with low initial soil moisture content than for events associated with higher initial soil moisture content. A sensitivity analysis indicates that the urban loss-model is relatively robust with regard to percentage runoff and imperviousness of the urban area.

THE POSSIBILITY OF IMPROVING SURFACE IRRIGATION WITH BLOCKED END ON SPARSE GRAPE TREES

Border system that applies water over the whole soil surface is a widely used method of surface irrigation in Egypt to irrigate grape farms. Furrow system can be used to lessen water applied per irrigation in distant parallel channels to partially wet the soil surface along with plants line. A field study was carried out in northern Egypt to authorize using distant furrows rather than borders as an improving irrigation system for grape farms on a clay loam soil with 1.3 g cm -3 bulk density during 2008 season in Shibin El-Kom area, Egypt. Border irrigation was practiced to apply 9.8, 12.0, and 15.5 m 2 /h inflow rate per unit width when gravimetric soil moisture content was initialized at 24.7%. A 9.8 m 2 /h per unit width was applied when soil moisture content by weight was initialized as 21.4, 24.7, and 27.1%. Inflow rates of 2.2, 3.0, 4.0 m 3 /h were applied by furrow irrigation at 25.1% initial moisture content by weight. Gravimetric initial moisture contents 22.7, 25.4, and 27.2% were initialized under furrow irrigation with 2.2 m 3 /h inflow rate. The results showed that the greater inflow rate or the wetter initial soil surface was applied, the smaller water advance time and the greater recession time were occurred. Infiltrated water depth was individually increased by decreasing either inflow rate or initial soil moisture content. Coefficient of variation as well as distribution and application efficiencies was generally improved by increasing inflow rate, initial soil moisture content, or storage phase time. Water use per day was ranged from 4.9 to 6.1 mm by border irrigation and from 2.8 to 3.6 mm by partially wetted furrow irrigation. Water saving was achieved as 39.5-49% by partially wetted furrow irrigation compared to border as practiced in grape farm. Grape yield was significantly improved with increasing inflow rate, initial moisture, and storage phase. Keyword: surface irrigation; evaluation; water distribution and efficiency; water use.