The first full projections of rainfall and streamflow in the “Fertile Crescent” of Middle East are presented in this paper. Up until now, this has not been possible due to the lack of observed data and the lack of atmospheric models with sufficient resolution. An innovative super-high-resolution (20-km) global climate model is employed, which accurately reproduces the precipitation and the streamflow of the present-day Fertile Crescent. It is projected that, by the end of this century, the Fertile Crescent will lose its current shape and may disappear altogether. The annual discharge of the Euphrates River will decrease significantly (29-73%), as will the streamflow in the Jordan River. Thus countermeasures for water shortages will become much more difficult.

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One of the common contributors to the uncertainty in any rainfall runoff model is the error distribution within the rainfall inputs. The uncertain rainfall introduces systematic bias in the estimated parameters. We present here the application of a method, known as simulation extrapolation (SIMEX), to ascertain the extent of parameter bias. SIMEX requires a knowledge of the standard error associated with the rainfall at any given time step. With this knowledge, it generates multiple sets of rainfall with artificially inflated error variance, and then assesses whether this leads to any trend in the resulting parameters. This trend is then extrapolated back to assess the most suitable parameter value when the input is error free. The applicability of the method is investigated using a synthetic example where rainfall uncertainty is multiplicative and temporally invariant. This paper ascertained the bias trend in three key storage parameters of the Sacramento Rainfall Runoff Model representing surface and subsurface flow mechanisms respectively. This initial investigation confirmed the stability of SIMEX for use in hydrological model specification studies; which hints the possibility of embedding this simple method to improve runoff estimation.

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The depth profile of ³⁶Cl/Cl ratio in groundwater was investigated in the Tsukuba Upland of central Japan. The obtained results clearly show the influence of bomb-produced ³⁶Cl; the highest ³⁶Cl/Cl ratio is about one order of magnitude greater than the natural background ratio (1 × 10^-13). The vertical distribution of ³⁶Cl is consistent with previous observations using ³H and Darcy’s law. From the profile, the total bomb-produced ³⁶Cl fallout in the upland is 2.3 × 10¹² atoms/m² after the correction for surface runoff (c.f. 2.4 × 10¹² atoms/m² at the Dye-3 site, Greenland) and a scaling factor of 0.96 was obtained (c.f. 2.5 based on the simplified latitudinal fallout distribution model). We then reconstructed the local fallout history of ³⁶Cl based on the Dye-3 data (scaled with a factor of 0.96 for the Tsukuba Upland) and the mean ³⁶Cl flux, produced in the atmosphere from cosmic rays and measured 30 atoms m^-2 s^-1 in the upland. The ratio of the maximum bomb-peak fallout to the average natural background flux of meteoric ³⁶Cl is consistent with that of measured data in Nepal. The result implies that the simplified latitudinal distribution model for ³⁶Cl deposition is not easily applicable for the prediction of the bomb-produced ³⁶Cl fallout pattern.

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This study examines rainfall-runoff characteristics of catchments underlain by granitic and sedimentary rock. Differences in bedrock geology and forest age for sedimentary rock catchments were considered. In granite catchment, the quick flow ratio was small and baseflow was sufficient even during dry conditions because of large water storage within the soil and the relatively homogeneous weathered bedrock. In sedimentary rock catchments, water that infiltrated to the soil and fractured bedrock drained quickly, causing large quick flow over short, rainstorm timescales. The peak flow was lower in sedimentary rock catchments with older forest where the soils were more developed over longer periods of forest growth. The differences among sedimentary rock catchments by forest age were smaller than the differences between granitic and sedimentary rock catchments. Bedrock geology is of primary importance for categorizing and identifying universal rainfall-runoff characteristics.

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This study modifies a Global River-flow model (GRiveT) to more realistically represent groundwater and river-flow processes and examines the effects of these modifications on the reproducibility of the hydrological processes. These modifications include assigning calibrated spatially distributed current speeds and implementing a groundwater scheme. A current speed calibration method is proposed to eliminate river discharge phase differences (RPDs) between the observation and the simulation. We performed nine-year integrations of the modified version of GRiveT. The experimental results were then compared with the observed data for 70 of the world’s major rivers. The proposed calibration method provides reasonable calibrated speeds that eliminate RPD for most of the 70 rivers considered. The calibration significantly improves the river discharge correlation coefficient and phase difference and improves the terrestrial water storage (TWS) correlation coefficient and phase difference to a lesser extent. However, there was little improvement to river discharge and TWS amplitudes. The implementation of the groundwater scheme improves river discharge and TWS correlation coefficients and phase differences for experiments without calibration. The calibration can compensate for the disadvantages of not implementing the groundwater scheme.

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A statistical approach that considers the bias and uncertainty of models is proposed for interpreting the simulated river discharge as a flood risk. A 29-year simulation was performed to estimate parameters of the Gumbel distribution for the probability of extreme discharge. The estimated discharge probability index (DPI) showed clear agreement with observed values. Even more strikingly, high DPI in the simulation corresponded to actual flood damage records. This indicates that the real-time simulation of the DPI could potentially provide flood warnings. This paper also suggests an application using the same statistical method for real-time flood risk prediction that overcomes the lack of sufficiently long simulation data through the use of a pre-existing long-term simulation to estimate statistical parameters. A preliminary flood risk prediction that used operational weather forecast data for 2003 and 2004 gave results similar to those of the 29-year simulation for the Typhoon Tokage (T0423) event on October 20th 2004, demonstrating the transferability of the technique to real-time prediction, which is differently biased.

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Water markets were expected to minimise the socioeconomic impact of reducing irrigators’ water entitlements in Australia’s Namoi Valley by providing a mechanism for reallocating water from inactive license holders to active irrigators. But survey responses show that this is an unlikely scenario as it appears as though there may be a number of influences acting on inactive license holders that are stronger than the desire for economic gain from participating in water markets. This research constructs a typology that aims to provide an explanatory framework for understanding what those influences might be. A better understanding of farmers’ attitudes and objectives; and of the motivations for their behaviour, is likely to lead to better policy design and more successful policy implementation. The implication for policy makers is that reducing irrigators entitlement based on their past usage, rather than equal reductions for all, will cause less disruption within the affected communities as this method places minimum reliance on the market as a reallocation mechanism.

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Staining substances have been widely used to visualize flow paths in soils, and recently dye concentrations in soil profiles are quantified using photographs. Fluorescent dye Uranine is one of the promising staining agents. The sorption properties of Uranine are needed to establish initial concentrations in applied solutions, determine Uranine mobility, and model solute transport. At least 65% of Uranine adsorption on subsoils from Okaya, Japan occurred after 1 h of shaking. Subsequently, equilibrium sorption was assessed for six different forest soil samples, including topsoil, subsoil, and a buried organic-rich layer. Adsorption in all soil samples was significantly reduced by adjusting initial solution pH to 13. Adsorption was greater in topsoil; however, it was not significantly correlated with soil organic matter. The buried organic-rich soil experienced intermediate adsorption compared to topsoil and subsoil samples. Equilibrium adsorption data for both topsoil and subsoil samples best fit the Freundlich isotherm. In subsoils, Uranine sorption was comparable to reported values for Pyranine and commonly used Brilliant Blue FCF dye, while adsorption in topsoil samples from these forests (up to 21.7% organic matter) was significantly higher than reported values for agricultural soils.

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This paper describes the development and assessment of global 0.5° near-surface atmospheric data from 1948 to 2006 at daily (for precipitation, snowfall, and specific humidity) to 3-hourly (for temperature, shortwave radiation, and longwave radiation) time scales, which can be used to drive land surface models. Using newly available monthly precipitation and temperature data extending to recent years, the variables were created by statistical methods, the parameters of which were obtained from available daily to 3-hourly observations. The daily precipitation developed in this paper produces reasonable numbers of precipitation days and heavy precipitation days, different from previous long-term meteorological data sets based on reanalysis. Together with its relatively high spatial resolution (0.5°) and availability of recent years, the newly obtained data may be preferred to other forcing data sets in case of hydrological and climate change studies, in particular if the study results are sensitive to daily variations in atmospheric conditions.

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We examined the influence of phenological changes in stomata on the seasonal variation of stomatal conductance using a Jarvis-type conductance model that included functions representing the active stomatal density and chlorophyll concentration of leaves. We studied the leaves of three 12-year-old oak trees (Quercus serrata). Stomatal conductance was measured under controlled ambient conditions (i.e., photosynthetic photon flux density, leaf temperature, and specific humidity deficit) in a chamber. Our analyses showed that low stomatal conductance could not be explained by environmental variables alone. Stomatal conductance decreased with increasing stomatal density, where the number of stomata included guard mother cells (GMC), in spring. On the other hand, time series of stomatal conductance showed a correlation with the increases in active stomatal density. Chlorophyll concentration was a good index of the low conductance in autumn, and the active stomata density was a good index of the leaf-unfolding period. These results implied that phenological progress of stomata must be included in land surface models for the accurate prediction of seasonal variations in water, energy, and CO₂ cycles.

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We produced a new gauge-based analysis of daily precipitation over Japan from 1981 to 2000 on a 0.01° grid. Wind-induced undercatch was adjusted at each observation station, and orographic effects were considered in the process of spatial interpolation from station data to the gridded product. The resulting gridded gauge-based analysis of precipitation was validated against observed river discharge data. The validation demonstrated that the product is reasonable, mostly because of the undercatch adjustment. Based on the resulting product, Japan receives nearly 2000 mm/year of precipitation on average, which is approximately 10% larger than commonly thought.

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Over the past two decades, many studies have reported the presence of soil pipes in hillslopes and their significant influence on rainfall-runoff processes. To analyze pipe flow mechanisms which have complex flow dynamics and interaction with water in the surrounding soil, this study proposed a numerical simulation model which combined a slot model with a three-dimensional saturated-unsaturated subsurface flow model. Soil matrix flow and pipe flow were regarded as separate flow systems and calculated using the individual governing equations, which are Richards equation and the dynamic flow equation. To validate the model, the simulations were conducted for three different conditions (no pipe, open pipe and closed pipe) and showed good agreement with experimental observation data.

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The present article reports the first investigation on the reproducibility of three land-surface hydrological variables (soil moisture, river discharge, and terrestrial water storage) in Japanese 25-year Reanalysis (JRA-25) by a system consisting of the Land Data Analysis (LDA) of JRA-25 and the modified version of a global river-flow model. JRA-25 well reproduces the seasonal cycles of observed soil moisture, river discharge, and terrestrial water storage. Detailed examinations revealed that the high reproducibility of the seasonal cycle of soil moisture originates from that of precipitation, that the low amplitude reproducibility for river discharge results from insufficient representation of the land-surface hydrology and insufficient reproducibility of the annual mean precipitation in JRA-25, and that the low amplitude reproducibility of terrestrial water storage predominantly results from insufficient representation of the land-surface hydrological model. An additional comparison in the reproducibility of soil moisture between JRA-25 and operational LDA reveals that the better reproducibility of soil moisture in JRA-25 does not always result from reasonable physical processes. The JRA-25 dataset should be used cautiously for studies in hydrology and meteorology, since the reproducibility varies with basins or areas.

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A series of numerical experiments were conducted in order to investigate the impact of global warming on snow amount in Japan during early winter. After confirming the accuracy of hindcast simulations for a High-Snow-Cover (HSC) year and a Low-Snow-Cover (LSC) year, dynamical downscaling experiments were conducted in order to make future projections using the Pseudo-Global-Warming method. The precipitation, snow depth, and surface air temperature of the hindcast simulations show good agreement with the AMeDAS station data. At the end of December, the decreasing ratios of snow water are more significant in areas with an altitude of less than 1,500 m. The increase in the air temperature is one of the major factors influencing the decrease in snow water since the present mean air temperature in most of these areas is near 0°C even in winter. On the other hand, the change in the mean areal precipitation due to global warming is less than 15% in both years.

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Global terrestrial snowfall was estimated for 59 years from 1948 to 2006 by applying gauge undercatch correction for snowfall and rainfall based on daily meteorological data and gauge type. Following gauge correction, global annual snowfall estimation increased from 9.4 to 12.3 × 10³ km³, while annual terrestrial precipitation increased from 112.8 to 119.6 × 10³ km³. Percentage of snowfall in total precipitation increased from 8.3 to 10.3% with gauge correction. The snowfall distinction method using wet-bulb temperature produced larger values for snowfall than those obtained using a 0°C threshold method and those from reanalysis-based products. In contrast, the increase in total precipitation was half of the increase obtained by using a climatology of correction coefficients from previous studies. The estimated 59-year time series of snowfall amount showed a downward trend after the mid-1980s, suggesting a decrease in snowfall associated with a warmer climate in recent decades.

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The fractal dimension H, which is frequency-dependent within Quasi-Biennial (QB) period, was explored to measure the noise characteristics of Niño 3.4 Sea Surface Temperature (SST), where “noise” specifies the cycles within QB such as the Tropospheric Biennial Oscillation (TBO). The results show that the oscillation pattern of H corresponds mostly to development of El Niño, particularly during two strong Tropical Pacific Decadal Oscillation (TDO) periods of 1894 to 1923 and 1978 to 2000. This represents a stochastic resonance mechanism when a positive-phase noise overlaps a stronger positive-phase of TDO. In this case, SST would exceed a critical value to trigger an El Niño. The mechanism provides a favorable condition by which the onset of El Niño becomes more sensitive to noise. Self-organized criticality (SOC) explains that a small disturbance on an uncertain system will result in an avalanche, including scale-invariance (scaling) and criticality (threshold) features. The results show that strong and medium El Niño events regularly show scaling within QB period especially after the 1970s. Therefore, scaling is a critical state for onset of a strong El Niño and noise modulation by SOC within QB period plays a significant role in the El Niño developments.

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