scholarly journals Diverse trends in observed pan evaporation in South Africa suggest multiple interacting drivers

2021 ◽  
Vol 117 (7/8) ◽  
Author(s):  
R. Arthur Chapman ◽  
Guy F. Midgley ◽  
Kathleen Smart
Keyword(s):  
South Africa ◽  
Water Resource Management ◽  
Open Water ◽  
Surface Friction ◽  
Tree Cover ◽  
Pan Evaporation ◽  
Alien Plant ◽  
Local Conditions ◽  
Global Dimming ◽  
Global Drivers

Planning for future water resource management in a warming climate is confounded when an expectation of increasing evaporation from open water surfaces with global warming is contradicted by observations of secular declines of pan evaporation. Decreasing pan evaporation has been observed globally – a trend which has been attributed variously to declines in wind run (‘global stilling’), declines in radiation (‘global dimming’) and increases in ambient humidity. This contrast between expectation and observation is known as the ‘evaporation paradox’. We evaluated trends in Symons pan evaporation from 154 pans across South Africa. Whilst 59 pans (38% of the 154) showed a statistically significant decrease in observed evaporation rates (p≤0.05), 30 (20%) showed an increase, and 65 (42%) showed no change. These results do not support simple attributions of trends to a common global cause. There is no spatially coherent pattern to trends across South Africa, suggesting that shifts in local drivers of evaporation confound expectations of secular trends due to global drivers. Changes in fetch conditions of the Symons pan installations may be implicated, whereby increasing tree density (through afforestation, alien plant invasion and woody thickening) increases surface friction, reducing wind run, and/or irrigation nearby, increasing local humidity. Correct attribution of the evaporation paradox to reduced wind run in South Africa must consider changing local conditions. Increased tree cover has been observed near a third of the South African Symons pans. Observed evaporation increases for one fifth of pans may implicate expected global drivers for pans where local fetch conditions have remained relatively constant.

scholarly journals A Remote Sensing Method to Monitor Water, Aquatic Vegetation, and Invasive Water Hyacinth at National Extents

2020 ◽  
Vol 12 (24) ◽  
pp. 4021
Author(s):  
Geethen Singh ◽  
Chevonne Reynolds ◽  
Marcus Byrne ◽  
Benjamin Rosman
Keyword(s):  
South Africa ◽  
Water Hyacinth ◽  
Aquatic Vegetation ◽  
Hierarchical Classification ◽  
Open Water ◽  
Google Earth ◽  
Species Discrimination ◽  
Landsat 8 ◽  
Forest Modelling ◽  
Alien Plant

Diverse freshwater biological communities are threatened by invasive aquatic alien plant (IAAP) invasions and consequently, cost countries millions to manage. The effective management of these IAAP invasions necessitates their frequent and reliable monitoring across a broad extent and over a long-term. Here, we introduce and apply a monitoring approach that meet these criteria and is based on a three-stage hierarchical classification to firstly detect water, then aquatic vegetation and finally water hyacinth (Pontederia crassipes, previously Eichhornia crassipes), the most damaging IAAP species within many regions of the world. Our approach circumvents many challenges that restricted previous satellite-based water hyacinth monitoring attempts to smaller study areas. The method is executable on Google Earth Engine (GEE) extemporaneously and utilizes free, medium resolution (10–30 m) multispectral Earth Observation (EO) data from either Landsat-8 or Sentinel-2. The automated workflow employs a novel simple thresholding approach to obtain reliable boundaries for open-water, which are then used to limit the area for aquatic vegetation detection. Subsequently, a random forest modelling approach is used to discriminate water hyacinth from other detected aquatic vegetation using the eight most important variables. This study represents the first national scale EO-derived water hyacinth distribution map. Based on our model, it is estimated that this pervasive IAAP covered 417.74 km2 across South Africa in 2013. Additionally, we show encouraging results for utilizing the automatically derived aquatic vegetation masks to fit and evaluate a convolutional neural network-based semantic segmentation model, removing the need for detection of surface water extents that may not always be available at the required spatio-temporal resolution or accuracy. The water hyacinth species discrimination has a 0.80, or greater, overall accuracy (0.93), F1-score (0.87) and Matthews correlation coefficient (0.80) based on 98 widely distributed field sites across South Africa. The results suggest that the introduced workflow is suitable for monitoring changes in the extent of open water, aquatic vegetation, and water hyacinth for individual waterbodies or across national extents. The GEE code can be accessed here.

scholarly journals Hydrology influences breeding time in the white-throated dipper

BMC Ecology ◽  
2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Anna L. K. Nilsson ◽  
Thomas Skaugen ◽  
Trond Reitan ◽  
Jan Henning L’Abée-Lund ◽  
Marlène Gamelon ◽  
...  
Keyword(s):  
Climate Change ◽  
River Discharge ◽  
Large Scale ◽  
Time Window ◽  
River System ◽  
Open Water ◽  
Local Conditions ◽  
Environmental Indices ◽  
Groundwater Levels ◽  
Breeding Time

Abstract Background Earlier breeding is one of the strongest responses to global change in birds and is a key factor determining reproductive success. In most studies of climate effects, the focus has been on large-scale environmental indices or temperature averaged over large geographical areas, neglecting that animals are affected by the local conditions in their home ranges. In riverine ecosystems, climate change is altering the flow regime, in addition to changes resulting from the increasing demand for renewable and clean hydropower. Together with increasing temperatures, this can lead to shifts in the time window available for successful breeding of birds associated with the riverine habitat. Here, we investigated specifically how the environmental conditions at the territory level influence timing of breeding in a passerine bird with an aquatic lifestyle, the white-throated dipper Cinclus cinclus. We relate daily river discharge and other important hydrological parameters, to a long-term dataset of breeding phenology (1978–2015) in a natural river system. Results Dippers bred earlier when winter river discharge and groundwater levels in the weeks prior to breeding were high, and when there was little snow in the catchment area. Breeding was also earlier at lower altitudes, although the effect dramatically declined over the period. This suggests that territories at higher altitudes had more open water in winter later in the study period, which permitted early breeding also here. Unexpectedly, the largest effect inducing earlier breeding time was territory river discharge during the winter months and not immediately prior to breeding. The territory river discharge also increased during the study period. Conclusions The observed earlier breeding can thus be interpreted as a response to climate change. Measuring environmental variation at the scale of the territory thus provides detailed information about the interactions between organisms and the abiotic environment.

scholarly journals Two Comprehensive and Practical Methods for Simulating Pan Evaporation Under Different Climatic Conditions in Iran

Water ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 2814
Author(s):  
Mohammad Hassan Dehghanipour ◽  
Hojat Karami ◽  
Hamidreza Ghazvinian ◽  
Zahra Kalantari ◽  
Amir Hossein Dehghanipour
Keyword(s):  
Genetic Algorithm ◽  
Water Resource Management ◽  
Three Dimensional ◽  
Climatic Conditions ◽  
Pan Evaporation ◽  
Linear Quadratic ◽  
Climate Type ◽  
Method Error ◽  
Basic Relationship ◽  
Quadratic Relationship

Evaporation from surface water plays a crucial role in water accounting of basins, water resource management, and irrigation systems management. As such, the simulation of evaporation with high accuracy is very important. In this study, two methods for simulating pan evaporation under different climatic conditions in Iran were developed. In the first method, six experimental relationships (linear, quadratic, and cubic, with two input combinations) were determined for Iran’s six climate types, inspired by a multilayer perceptron neural network (MLP-NN) neuron and optimized with the genetic algorithm. The best relationship of the six was selected for each climate type, and the results were presented in a three-dimensional graph. The best overall relationship obtained in the first method was used as the basic relationship in the second method, and climatic correction coefficients were determined for other climate types using the genetic algorithm optimization model. Finally, the accuracy of the two methods was validated using data from 32 synoptic weather stations throughout Iran. For the first method, error tolerance diagrams and statistical coefficients showed that a quadratic experimental relationship performed best under all climatic conditions. To simplify the method, two graphs were created based on the quadratic relationship for the different climate types, with the axes of the graphs showing relative humidity and temperature, and with pan evaporation, were drawn as contours. For the second method, the quadratic relationship for semi-dry conditions was selected as the basic relationship. The estimated climatic correction coefficients for other climate types lay between 0.8 and 1 for dry, semi-dry, semi-humid, Mediterranean climates, and between 0.4 and 0.6 for humid and very humid climates, indicating that one single relationship cannot be used to simulate pan evaporation for all climatic conditions in Iran. The validation results confirmed the accuracy of the two methods in simulating pan evaporation under different climatic conditions in Iran.

Evaluating the cost-effectiveness of invasive alien plant clearing: A case study from South Africa

2012 ◽  
Vol 155 ◽  
pp. 128-135 ◽  
Author(s):  
Matthew M. McConnachie ◽  
Richard M. Cowling ◽  
Brian W. van Wilgen ◽  
Dominic A. McConnachie
Keyword(s):  
South Africa ◽  
Cost Effectiveness ◽  
Alien Plant ◽  
Invasive Alien Plant ◽  
The Cost

SOUTH AFRICA'S RESERVE: CHALLENGES AND RECOMMENDATIONS FOR IMPLEMENTING SUSTAINABLE DEVELOPMENT POLICIES

2006 ◽  
Vol 08 (01) ◽  
pp. 61-83 ◽  
Author(s):  
ALISON BODURTHA QUA-ENOO ◽  
KATE SCHENDEL ◽  
NEVIL QUINN
Keyword(s):  
South Africa ◽  
Sustainable Development ◽  
Resource Management ◽  
Water Resource ◽  
Water Resource Management ◽  
Political Support ◽  
Successful Implementation ◽  
Human Needs ◽  
Challenges And Opportunities ◽  
Key Issues

South Africa introduced a visionary policy for water resource management in 1998. The South African National Water Act (Act 36 of 1998) contains several innovative mechanisms with the potential to transform water resource management within the country and abroad. The Reserve is one of these innovations, guaranteeing a basic water requirement for both human needs and ecosystem health. This article discusses the process of Reserve determination and implementation in South Africa and identifies challenges and opportunities for successful implementation. Based on the perceptions of 28 water managers, consultants, and researchers, the key issues and recommendations for improving implementation are presented. The major findings indicate that political support, the capacity of the implementing organization, supporting policies, strong linkages between policy actors and effective monitoring programs are key issues in the successful implementation of sustainable development policy mechanisms.

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