In this study, the seasonal transition of precipitation over the middle and lower reaches of the Yang-tze River Valley (YRV) from late spring to early summer is investigated. The results show that the seasonal transit...In this study, the seasonal transition of precipitation over the middle and lower reaches of the Yang-tze River Valley (YRV) from late spring to early summer is investigated. The results show that the seasonal transition of precipitation exhibits multi-modes. One of these modes is characterized by an abrupt transition from drought to flood (ATDF) over the middle and lower reaches of the YRV in the seasonal transition of precipitation. It is shown that the ATDF event from May to June 2011 is simply one prominent case of the ATDF mode. The ATDF mode exhibits an obvious decadal variability. The mode has occurred more frequently since 1979, and its amplitude has apparently strengthened since 1994. From the climatic view, the ATDF mode configures a typical seasonal circulation transition from winter to summer, for which the winter circulations are prolonged, and the summer circulations with the rainy season are built up early over the YRV.展开更多
Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in ...Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.展开更多
Recurrent droughts and occasional floods are the facts of life in drylands. The presence of innumerable societies in deserts is the living proof that even the extremely dry environments are livable; the secret is how ...Recurrent droughts and occasional floods are the facts of life in drylands. The presence of innumerable societies in deserts is the living proof that even the extremely dry environments are livable; the secret is how to adapt to the situation. Floodwater management, the most important art of sedentarized desert dwellers, is the secret of living with deserts. Floodwater irrigation alone, or in combination with the artificial recharge of groundwater （ARG）, has sustained the Persians for millennia. The scientists at the Kowsar Floodwater Spreading and Aquifer Management Research, Training and Extension Station in the Gareh Bygone Plain have been working since January 1983 to revive this ancient art and upgrade it to the level of science. A summary of important findings is provided as follows： 1. Debris cones and coarse alluvial fans are the best places for the ARG as they provide the potential aquifer for groundwater storage. The recharged water may be used for irrigation on the lower lying, fine alluvium; 2. Flood is not a proverbial curse but a blessing in disguise, and the turbid floodwater is the best resource for the sustainable development of drylands; 3. Translocation of fine clay minerals eventually makes the vadose zone impermeable. Planting deep-rooted, drought-resistent trees and shrubs, and introducing sowbugs （Hemilepistus shirazi Schuttz） are reliable methods to increase infiltration rate and the saturated hydraulic conductivity of the ARG systems; 4. The moving sand stabilization is best achieved by spreading turbid floodwater onto them. Establishing of living windbreaks and planting of fodder trees and shrubs turn a sand menace into a verdant pasture; 5. The 10 year average of native forage yield in the ARG systems has been 445 kg·ha^-1·year^-1 as opposed to 92 kg·ha^-1.year^-1 for the control. At 4×4 m^2 spacing, Atriplex lentiformis （Torr.） Wats. can annually yield 1500 kg ha^-1 of dry matter and support 3 heads of sheep; 6. The stem- and fuel wood yield of 18 year old Eucalyptus camaldulensis Dehnh. in the ARG system have been 4,684 and 781 kg·ha^-1.year^-1, respectively. The mean annual carbon sequestration of this tree has been 2.975 tons per ha; 7.Up to 80% of the diverted floodwaters reach the unconfined aquifer. As evaporation practically wastes large volumes of water in surface reservoirs, storing water underground is logical in deserts; 8. The high evaporation rate, the large sediment load, the environmental hazards, the undesirable social costs, the long time needed for the different phases of study, and the very large price tag make dam building the most hydro-illogical choice in deserts where the ARG is practicable; 9. Each 5.5 ha of the irrigated farm provides income for a family of 7.64 member and 0.38 employment opportunities for a farm hand. On average, 4-ha of an ARG system provides one full time job for irrigation farmers. The benefit： cost ratio for this project is 22; 10. The number of wells in the area affected by the ARG activities has increased lo-fold to 130 wells, the irrigated area has increased 8-fold to 1,193 ha, and 345 job opportunities have been created in 4 villages that surround the Station.展开更多
The extraordinary rainfall occurred in the small river basin （called Asano River） of Kanazawa city, Ishikawa prefecture middle part of Japan, July 2008. The center of the city was affected by severe damages by the b...The extraordinary rainfall occurred in the small river basin （called Asano River） of Kanazawa city, Ishikawa prefecture middle part of Japan, July 2008. The center of the city was affected by severe damages by the big flood due to the extraordinary rainfall. This study aims to make clear the probability of the extraordinary rainfall, the mechanism of the flood, the flood fighting activities etc. and to prepare to the future big flood. For this purposes, the analysis of probability of rainfall events is carried out by use of three methods. They are Gumbel method, Hazen plot and Momentum method. The return period is estimated 250 years. Next runoff analysis by use of the Tank model method was carried out. This model consists of several series of rainfall storage tanks. The upper tank corresponds to surface runoff and the lower tank corresponds to inter runoff and ground water runoff. The result shows that the observed and simulated discharge is similar. So the future flood by the extraordinary rainfall events is able to predict the amounts of the flood. Finally, the problem of the flood fighting activity is cleared for the safety of the people in the river basin.展开更多
The paper deals with the impact of land use changes on water regime. An assessment was carried out in order to determine the extent to which the main components of the water balance on the experimental catchment Vsemi...The paper deals with the impact of land use changes on water regime. An assessment was carried out in order to determine the extent to which the main components of the water balance on the experimental catchment Vseminka have been influenced by land use changes （region Vsetinske Hills, the Czech Republic）. For this reason, the water balance model WBCM-5 was implemented for the period of 30 years in a daily step, with particular focus on the simulation of the components of direct runoff and of subsurface water recharge. In the selected years of the period 1980-2009, major changes were made in land use and significant fluctuation of rainfall-runoff regimes were observed （e.g. dry year 1992, flood year 1997 and normal year 2009）. After WBCM-5 parameter calibration it was observed that some water balance components can change in relation to substantial land use changes, even up to dozens of percent in a balance-consideration, i.e. in daily, monthly and yearly or decadal values, specifically as far as the components of interception and also of direct runoff and of subsurface water recharge are concerned. However, a different situation appeared during the investigation of significant short-term rainfall-runoff processes. There were about seven real flood events during the same period on the same catchment which were analysed using the KINFIL-2 model （time step 0.5 hr）. Land use change, positive or negative scenarios, were also analysed during this period. As opposed to long-term water balance analyses, only a 10% difference in the hydrograph peak and volume was observed. In summary, the authors have shown that it is always important to distinguish a possible land use change impact on either long-term balance or short-term runoff. Otherwise, as often found in over simplified commentaries on flood events in the mass media, the actual impact of land use changes on water regime may be misunderstood.展开更多
基金supported by the National Basic Research Program of China (Grant No.2009CB421401)the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)+1 种基金the National Natural Science Foundation of China (Grant No. 40975022)the Special Scien-tific Research Fund of the Meteorological Public Welfare Profession of China (Grant No. GYHY200906018)
文摘In this study, the seasonal transition of precipitation over the middle and lower reaches of the Yang-tze River Valley (YRV) from late spring to early summer is investigated. The results show that the seasonal transition of precipitation exhibits multi-modes. One of these modes is characterized by an abrupt transition from drought to flood (ATDF) over the middle and lower reaches of the YRV in the seasonal transition of precipitation. It is shown that the ATDF event from May to June 2011 is simply one prominent case of the ATDF mode. The ATDF mode exhibits an obvious decadal variability. The mode has occurred more frequently since 1979, and its amplitude has apparently strengthened since 1994. From the climatic view, the ATDF mode configures a typical seasonal circulation transition from winter to summer, for which the winter circulations are prolonged, and the summer circulations with the rainy season are built up early over the YRV.
基金supported by funding from the National Research Foundation to C. Boucher and the VSB Funds (the Netherlands) to E. Siebenadditional funding from the Water Research Commission
文摘Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.
文摘Recurrent droughts and occasional floods are the facts of life in drylands. The presence of innumerable societies in deserts is the living proof that even the extremely dry environments are livable; the secret is how to adapt to the situation. Floodwater management, the most important art of sedentarized desert dwellers, is the secret of living with deserts. Floodwater irrigation alone, or in combination with the artificial recharge of groundwater （ARG）, has sustained the Persians for millennia. The scientists at the Kowsar Floodwater Spreading and Aquifer Management Research, Training and Extension Station in the Gareh Bygone Plain have been working since January 1983 to revive this ancient art and upgrade it to the level of science. A summary of important findings is provided as follows： 1. Debris cones and coarse alluvial fans are the best places for the ARG as they provide the potential aquifer for groundwater storage. The recharged water may be used for irrigation on the lower lying, fine alluvium; 2. Flood is not a proverbial curse but a blessing in disguise, and the turbid floodwater is the best resource for the sustainable development of drylands; 3. Translocation of fine clay minerals eventually makes the vadose zone impermeable. Planting deep-rooted, drought-resistent trees and shrubs, and introducing sowbugs （Hemilepistus shirazi Schuttz） are reliable methods to increase infiltration rate and the saturated hydraulic conductivity of the ARG systems; 4. The moving sand stabilization is best achieved by spreading turbid floodwater onto them. Establishing of living windbreaks and planting of fodder trees and shrubs turn a sand menace into a verdant pasture; 5. The 10 year average of native forage yield in the ARG systems has been 445 kg·ha^-1·year^-1 as opposed to 92 kg·ha^-1.year^-1 for the control. At 4×4 m^2 spacing, Atriplex lentiformis （Torr.） Wats. can annually yield 1500 kg ha^-1 of dry matter and support 3 heads of sheep; 6. The stem- and fuel wood yield of 18 year old Eucalyptus camaldulensis Dehnh. in the ARG system have been 4,684 and 781 kg·ha^-1.year^-1, respectively. The mean annual carbon sequestration of this tree has been 2.975 tons per ha; 7.Up to 80% of the diverted floodwaters reach the unconfined aquifer. As evaporation practically wastes large volumes of water in surface reservoirs, storing water underground is logical in deserts; 8. The high evaporation rate, the large sediment load, the environmental hazards, the undesirable social costs, the long time needed for the different phases of study, and the very large price tag make dam building the most hydro-illogical choice in deserts where the ARG is practicable; 9. Each 5.5 ha of the irrigated farm provides income for a family of 7.64 member and 0.38 employment opportunities for a farm hand. On average, 4-ha of an ARG system provides one full time job for irrigation farmers. The benefit： cost ratio for this project is 22; 10. The number of wells in the area affected by the ARG activities has increased lo-fold to 130 wells, the irrigated area has increased 8-fold to 1,193 ha, and 345 job opportunities have been created in 4 villages that surround the Station.
文摘The extraordinary rainfall occurred in the small river basin （called Asano River） of Kanazawa city, Ishikawa prefecture middle part of Japan, July 2008. The center of the city was affected by severe damages by the big flood due to the extraordinary rainfall. This study aims to make clear the probability of the extraordinary rainfall, the mechanism of the flood, the flood fighting activities etc. and to prepare to the future big flood. For this purposes, the analysis of probability of rainfall events is carried out by use of three methods. They are Gumbel method, Hazen plot and Momentum method. The return period is estimated 250 years. Next runoff analysis by use of the Tank model method was carried out. This model consists of several series of rainfall storage tanks. The upper tank corresponds to surface runoff and the lower tank corresponds to inter runoff and ground water runoff. The result shows that the observed and simulated discharge is similar. So the future flood by the extraordinary rainfall events is able to predict the amounts of the flood. Finally, the problem of the flood fighting activity is cleared for the safety of the people in the river basin.
文摘The paper deals with the impact of land use changes on water regime. An assessment was carried out in order to determine the extent to which the main components of the water balance on the experimental catchment Vseminka have been influenced by land use changes （region Vsetinske Hills, the Czech Republic）. For this reason, the water balance model WBCM-5 was implemented for the period of 30 years in a daily step, with particular focus on the simulation of the components of direct runoff and of subsurface water recharge. In the selected years of the period 1980-2009, major changes were made in land use and significant fluctuation of rainfall-runoff regimes were observed （e.g. dry year 1992, flood year 1997 and normal year 2009）. After WBCM-5 parameter calibration it was observed that some water balance components can change in relation to substantial land use changes, even up to dozens of percent in a balance-consideration, i.e. in daily, monthly and yearly or decadal values, specifically as far as the components of interception and also of direct runoff and of subsurface water recharge are concerned. However, a different situation appeared during the investigation of significant short-term rainfall-runoff processes. There were about seven real flood events during the same period on the same catchment which were analysed using the KINFIL-2 model （time step 0.5 hr）. Land use change, positive or negative scenarios, were also analysed during this period. As opposed to long-term water balance analyses, only a 10% difference in the hydrograph peak and volume was observed. In summary, the authors have shown that it is always important to distinguish a possible land use change impact on either long-term balance or short-term runoff. Otherwise, as often found in over simplified commentaries on flood events in the mass media, the actual impact of land use changes on water regime may be misunderstood.
