Study On Climato-hydrological Models Incorporating Groundwater Processes At The Catchment Scale

Climate change dominated by global warming,has accelerated changes in hydrological factors at the global and regional scales.Climato-hydrological model at catchment scale is the most important method and tool to study the water cycle of the basin.In previous studies,land-surface hydrological processes have been the focus of attention,and groundwater processes are often ignored or simply considered because of their complexity and invisibility.Due to the inconsistency in the division of surface watersheds and groundwater flow systems,few people explain the relationship between watershed and groundwater flow systems conceptually and mechanically,and further identify a three-dimensional hydrological cycle that unifies surface water and groundwater.This paper studies the above issues through theoretical analysis and practical cases.According to propose a concise model on the basic of the proportionality hypothesis,a non-parameter actual evapotranspiration formula with soil-plant-atmosphere continuum at annual and catchment scale was obtained,which extended the Budyko framework at mean annual scale to inter-annual scale.A new tri-parameter climate-hydrological model(bcd model)was developed using this non-parameter formula.The above innovative theory and model were successfully applied to the NLRB in Nebraska,USA,and it was obtained that the movement path of the interannual hydrological change of the basin in the Budyko space was different from any classic Budyko curve.Taking the change in water storage into account in the interannual hydrological process to extend the Budyko framework,we derived a theoretical analytical formula for the hydrological sensitivity coefficients.The bcd model was improved by condisering the effects of cropland.It was successfully applied to twelve catchments in Illinois,USA,and it was found that the croplands significantly increased the actual evapotranspiration and the sensitivity of runoff to climate change.The correlation between annual C/P and E_p/P is negative linearly with weak influence of cropland.The original bcd model used for annual time scale was successfully applied to the monthly time scale and verified in two catchments in the Ordos Plateau.At the same time,the effect of groundwater-depend evapotranspiration was further incorporated into the bcd model to obtain the bcd-GE model,and it was successfully applied to the six catchments in the Ordos Plateau.We also found that when the effect of groundwater-depend evapotranspiration was significant,the standard Budyko formula was not applicable for the interannual variablity of catchment water balance.The saturated-unsaturated 2D theoretical model between two rivers in the unconfined aquifer was constructed,and it proved that the highest point of the water table may not be the groundwater divide.Compared with the traditional definition of the groundwater divide,the actual groundwater divide is closer to the higher river.The catchment area of the high river obtained using the highest point of the water table would be overestimated,with an error of up to~50%,while the catchment area of the low river would be underestimated,whose error is usually less than~15%.According to establish the 2D theoretical model for simple and complex river basins respectively,we found that in addition to traditional groundwater flow systems proposed by Tóth(1963),a new type of groundwater flow system,named off-water-table flow system,existed conditionally.This flow system did not get recharge from the water table,but it could transport water from one river to another.The development of the off-water-table flow system depended on the penetration depth of rivers,infiltration recharge and hydraulic characteristics of the basin.Based on the developed climato-hydrological model and the water balance method combined with remote sensing evapotranspiration products,it was indirectly proven that interbasin groundwater flow existed in the current Hailiutu river.Using three-dimensional groundwater flow numerical simulation,a new method for automatically drawing groundwater watershed was further proposed,which directly proved that interbasin groundwater flow existed.The divisions of watershed and groundwater flow systems were completely unified in a three-dimensional hydrological cycle space.The paper also quantitatively proved that the runoff observed by the hydrological station in Hailiutu river consisted of four parts:surface runoff(11%),local groundwater flow(43%),intermediate groundwater flow(15%),and regional groundwater flow(31%).Finally,comprehensive analysis showed that that the interbasin groundwater flow in the Budyko space would have a significant impact on the climato-hydrological process.The paper is helpful for scientific understanding of the surface water and groundwater cycle.