Performance measures (PMs) and corresponding performance evaluation criteria (PEC) are important aspects of calibrating and validating hydrologic and water quality models and should be updated with advances in modeling science. We synthesized PMs and PEC from a previous special collection, performed a meta-analysis of performance data reported in recent peer-reviewed literature for three widely published watershed-scale models (SWAT, HSPF, WARMF), and one field-scale model (ADAPT), and provided guidelines for model performance evaluation. Based on the synthesis, meta-analysis, and personal modeling experiences, we recommend coefficient of determination (R2; in conjunction with gradient and intercept of the corresponding regression line), Nash Sutcliffe efficiency (NSE), index of agreement (d), root mean square error (RMSE; alongside the ratio of RMSE and standard deviation of measured data, RSR), percent bias (PBIAS), and several graphical PMs to evaluate model performance. We recommend that model performance can be judged satisfactory for flow simulations if monthly R2 0.70 and d 0.75 for field-scale models, and daily, monthly, or annual R2 0.60, NSE 0.50, and PBIAS ≤ ±15% for watershed-scale models. Model performance at the watershed scale can be evaluated as satisfactory if monthly R2 0.40 and NSE 0.45 and daily, monthly, or annual PBIAS ≤ ±20% for sediment; monthly R20.40 and NSE 0.35 and daily, monthly, or annual PBIAS ≤ ±30% for phosphorus (P); and monthly R2 0.30 and NSE 0.35 and daily, monthly, or annual PBIAS ≤ ±30% for nitrogen (N). For RSR, we recommend that previously published PEC be used as detailed in this article. We also recommend that these PEC be used primarily for the four models for which there were adequate data, and used only with caution for other models. These PEC can be adjusted within acceptable bounds based on additional considerations, such as quality and quantity of available measured data, spatial and temporal scales, and project scope and magnitude, and updated based on the framework presented herein. This initial meta-analysis sets the stage for more comprehensive meta-analysis to revise PEC as new PMs and more data become available.

Hydrologic and Water Quality Models: Performance Measures and Evaluation Criteria

Nutrient requirements of beef cattle

Soil and Water : Physical Principles and Processes  By Daniel Hillel (Physiological Ecology: a Series of Monographs and Treatises) Pp xiv + 288 (Academic: New York and London, January 1971) $14; £655

Soil and Water

A review of methods and applications of the geometric characterization of tree crops in agricultural activities

. Hydrologic and water quality (H/WQ) models are widely used to support site-specific environmental assessment, design, planning, and decision making. Calibration and validation (C/V) are fundamental processes used to demonstrate that an H/WQ model can produce suitable results in a particular application. However, the lack of comprehensive guidelines has led to the use of ad hoc, inconsistent, and incomplete C/V processes, which have made it difficult to interpret the myriad of published modeling studies, reduced the utility of many modeling applications, and slowed the advancement of H/WQ modeling. The objective of this article is to provide a generalized structure and process to assist modelers in developing a C/V strategy for H/WQ modeling applications. These best practice recommendations were developed based on an expansive review of the modeling literature, including a special collection of articles on H/WQ model calibration, validation, and use, as well as extensive discussion and debate among the authors. The model C/V recommendations include careful consideration, execution, and documentation of the following elements: (1) goals of model use, (2) data and parameters used in C/V, and (3) model C/V processes. Considerations in element 3 include the warm-up period, C/V strategy complexity, C/V process staging, spatiotemporal allocation of C/V comparison data, manual vs. automatic C/V, and additional diagnostics. Notable examples from the literature are provided for each strategy element. The comprehensive C/V strategy described herein will allow for better interpretation of future modeling studies, improved utility of modeling applications, and more systematic advancement of H/WQ models.

A Recommended Calibration and Validation Strategy for Hydrologic and Water Quality Models

In watersheds where land use and land cover changes take place over the modeling period, using a single land use geospatial dataset is not a true representation of the watershed condition. This article describes development of SWAT2009_LUC, a computer-based, geospatial tool that ingests multiple land use/land cover geospatial datasets and other associated information interactively and activates the land use change (LUC) module in the latest release of the Soil and Water Assessment Tool (SWAT 2009). The geospatial tool was tested in an urbanizing watershed in northwest Arkansas by using three temporal land use geospatial data layers acquired during 1999, 2004, and 2006. The results show that the land use distribution generated by the tool was consistent with the input land use layer for each year and was updated correctly during the model run. Model simulations with and without the activation of the LUC module showed that groundwater was underpredicted by up to 15%, while surface runoff was overpredicted by up to 13% at the subwatershed scale when a single post-development land use layer was used. Overall, the results showed that activating the LUC module using the SWAT2009_LUC tool improves the spatial and temporal hydrological responses from the SWAT 2009 model.

SWAT2009_LUC: A Tool to Activate the Land Use Change Module in SWAT 2009

The purpose of this article is to highlight the limitations of water-sensitive paper in characterizing spray droplet distribution and deposition in field application.  Spatial distributions of spray droplets discharged from an airblast sprayer were sampled on pairs of absorbent paper (AP) and water-sensitive paper (WSP) targets at several distances from the sprayer.  Spray solutions, containing a fluorescent tracer, were discharged from two nozzle sizes to achieve low and high volume rates commonly used in citrus applications.  Spray deposits on AP targets were measured by fluorometry and spray coverage areas on WSP cards were assessed by three independent image analysis systems.  Generally, there were good correlations ( R 2 = 0.9085 to 0.9748) among the three imaging systems in measuring WSP percent area coverage.  Lower volume rate (smaller droplets) provided more useful WSP targets than higher volume rate (larger droplets). Overall, there were somewhat weak correlations between WSP area coverage and AP spray deposition measurements.  Volume median diameter and number of droplet stains on WSP cards, obtained by only two imaging systems, showed noticeable differences between the measurements of the two systems.  Keywords: WSP, image analysis, spray volume rate, spray coverage, spray droplet size

Assessment of spray distribution with water-sensitive paper

This article describes a modeling approach for prioritizing 12-digit hydrologic unit code subwatersheds for the Illinois River Drainage Area in Arkansas (IRDAA) watershed utilizing the soil and water assessment tool (SWAT) model output for sediment, total phosphorus (TP), and nitrate-nitrogen (NO3-N). The model was calibrated and validated at seven locations for total flow, base flow, and surface runoff and at three locations for water quality outputs. A multi-objective function consisting of percent relative error (RE), Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS), coefficient of determination (R2), and ratio of the root mean square error to the standard deviation of measured data (RSR) was used to guide model evaluations. The resulting priority subwatersheds comprised only 24% of the total area of the watershed but contributed 49% of sediment, 33% of TP, and 27% of NO3-N simulated loadings. Statistical relationships between priority subwatersheds and their various characteristics assisted with supporting the prioritization results. For the IRDAA, this approach produced results that could assist watershed management agencies in optimizing allocation of limited resources in addressing water quality issues.

Naresh Pai

Papers

Hydrologic and Water Quality Models: Performance Measures and Evaluation Criteria

A Recommended Calibration and Validation Strategy for Hydrologic and Water Quality Models

SWAT2009_LUC: A Tool to Activate the Land Use Change Module in SWAT 2009

Assessment of spray distribution with water-sensitive paper

Identifying Priority Subwatersheds in the Illinois River Drainage Area in Arkansas Watershed Using a Distributed Modeling Approach