Downward approach to hydrological prediction

Abstract

Abstract:This paper presents an overview of the 'downward approach' to hydrologic prediction and attempts to provide a context for the papers appearing in this special issue. The downward approach is seen as a necessary counterpoint to the mechanistic 'reductionist' approach that dominates current hydrological model development. It provides a systematic framework to learning from data, including the testing of hypotheses at every step of analysis. It can also be applied in a hierarchical manner: starting from exploring first-order controls in the modelling of catchment response, the model complexity can then be increased in response to deficiencies in reproducing observations at different levels. The remaining contributions of this special issue present a number of applications of the downward approach, including development of parsimonious water balance models with changing time scales by learning from signatures extracted from observed streamflow data at different time scales, regionalization of model parameters, parameterization of effects of sub-grid variability, and standardized statistical approaches to analyse data and to develop model structures. This review demonstrates that the downward approach is not a rigid methodology, but represents a generic framework. It needs to play an increasing role in the future in the development of hydrological models at the catchment scale.

Groundwater and Surface Water Interaction at the Regional-scale – A Review with Focus on Regional Integrated Models

“…Kirchner (2006) and McDonnell et al (2007) suggest that the governing equations that apply in small scale physics might not adequately describe large scale hydrological responses in heterogeneous systems. Several authors have tried to further conceptualise and formalise the different significance and relevance at different scales as well as in different environments, landscapes and climates and to compile this into a theory of dominant processes (Grayson and Bloeschl 2000;Sivakumar 2004;Sivakumar 2008;Sivapalan et al 2003). The question of whether or not processes loose or gain relevancy at the large scale was already been raised in the preceding sections.…”

Comparing two tools for ecosystem service assessments regarding water resources decisions

“…However, this large amount of information would likely overwhelm decision-makers who often ask for simple indices to assist in making decisions. We also note that hydrologists debate the appropriate scales of representation for hydrologic processes [e.g., Sivapalan et al, 2003], so it may not be realistic to represent all scales well within one model . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 Figure 3 illustrates one suggested way forward; it couples the temporal and spatial scales of distinct ES decision contexts with the ability of models to provide information at these scales.…”

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

“…Combination of these bottom-up and top-down approaches can help understand the dominant control on catchment evapotranspiration at different time scales. The top-down approach in hydrology was first introduced by Klemes (1983) and extended further by Sivapalan and coworkers as outlined in Sivapalan et al (2003). This approach was used to investigate the hydrological response at long temporal scale and large spatial scale (e.g.…”

“…to apply the time-honored scientific method". Sivapalan et al (2003) also anticipated that "in the near future, studies that address the same problem by both approaches at the same time will make a significant impact on a better understanding of hydrologic prediction issues". Based on the previous research, this chapter attempts to build the connection between the top-down and bottom-up approach and to understand the dominant factors on catchment evapotranspiration at different time scales using a distributed physically-based hydrological model and a simple water-energy balance model.…”