Agricultural groundwater management strategies and seasonal climate forecasting: perceptions from Mogwadi (Dendron), Limpopo, South Africa

This paper explores the agricultural groundwater management system of Mogwadi (Dendron), Limpopo, South Africa – anarea associated with intensive use of hard rock aquifers for irrigation – and the potential contribution of seasonal forecasts. These relatively shallow aquifers are often perceived as ‘ self-regulating ’ ,yetclimatevariabilityandinfrequentrechargeepisodesraisethequestionofwhetherseasonal forecasting could contribute to more sustainable groundwater use. Hydro-meteorological observations, interviews and repeat focus groups with commercial farmers were used to examine this question for the 2014 – 15 rainfall season, with follow-up interviews during the 2015 – 16 El Niño season. Two long-term borehole series showed effects of episodic recharge events and management interventions. Comparison of formal and informal management practices highlighted important contrasts: a perceived lack of formal coordination within governing bodies, contrary to high levels of informal coordination between farmers despite a persistent ‘ tragedy of the commons ’ problem. Seasonal forecast use was limited due to lack of awareness and understanding of their relevance, low credibility and trust of forecasts, and poor dissemination. Farmers expressed increased interest in such information after the 2015 – 16 drought, if tailored to their needs. Increased uptake is, however, contingent on complementary groundwater monitoring network improvements and enhanced cooperation between stakeholder groups.


INTRODUCTION South Africa's groundwater and climate variability
Much of southern Africa has a semi-arid rainfall regime (400-650 mm yr À1 ) with high inter-annual variability, presenting challenges for water resources management in the region. Regional stream flows are unevenly distributed and display high levels of variability and widespread ephemeral character across a range of spatial and temporal scales (Conway et al. ).
High potential evapotranspiration results in exceptionally low conversion of rainfall to runoff (e.g., on average 5.1% in the Orange and Limpopo River Basins (Ashton & Hardwick ). Extensive regions within Africa regularly experience prolonged droughts that are often followed by intense rainfall events. In East Africa (Tanzania), highly episodic recharge events have been observed to occur from anomalously intense seasonal rainfall associated with the El Niño-Southern Oscillation and the Indian Ocean Dipole modes of climate variability (Taylor et al. ). This suggests nonlinear relationships between rainfall and recharge. However, apart from isolated case studies, the interactions between climate variability (on daily to seasonal timescales), recharge and groundwater storage are generally poorly understood, particularly in semi-arid and southern African contexts.
It has been argued that more use of groundwater is critical in helping communities and countries build resilience to climate change and its effects on variability in runoff and recharge, yet there is limited knowledge of African groundwater resources and their response to climate variability and change (Mac-Donald et al. , ). Groundwater resources are also seen as increasingly important in drought adaptation in sub-Saharan Africa by providing a buffer to surface water during dry seasons or drought (Hetzel et al. ; Braune & Xu ). However, policy response to drought in the region is generally short-term and reactive with ad-hoc expansion of groundwater drilling and abstraction, thus undermining groundwater's potential role in long-term integrated planning for water security (Wellfield Consulting Services & British Geological Survey ).
Shallow (less than 100 m deep) aquifers are frequently perceived as 'self-regulating', indicating that the inherent relatively small storage volume will be the key constraining factor putting a break on pumping, as opposed to deep and large-storage aquifers that will not, in the short term, show signs of physical exhaustion (Scanlon et al. ). Similarly, these aquifers will relatively easily and naturally recuperate during large recharge events. Hence, it could be argued that pro-active management is less dire. This is particularly the case for hard rock aquifers that typically display shallow and fractured characteristics.
However, these aquifers underlie relatively large population densities across southern Africa and are particularly prone to drought, and therefore represent vulnerable contexts for water security (Villholth et al. ). Where climate variability is high, recharge episodes can be infrequent and subsequent drought leads to extra pressure on aquifers, raising questions about the need for and suitability of additional management efforts. Such efforts include seasonal climate forecasting, which could enhance the sustainable use of these aquifers, in particular their use as a buffer during periods of drought.

Seasonal forecasts and agricultural water use
The South African agricultural sector faces chronic stress associated with extreme weather events and multi-year climate variability, yet adoption of seasonal climate information in agricultural decision-making has been limited (Haigh et al. ). This is paradoxical since farmers in South Africa tend to respond to seasonal variability rather than projections of future climatic change (Thomas et al.

).
Seasonal climate forecasts provide outlooks of rainfall and temperature for the rainy season of a region, typically produced at least once a month, in advance of the next rainy season progressively as a three-month average (Johnston ). They provide early warnings of dry conditions with implications for climate-sensitive sectors. Such forecasts have been identified as a useful entry-point for addressing climate change and variability by dealing with short-term climate-related problems, and building capacity to utilise climate information (Ziervogel et al. ; Conway ). This is particularly pertinent in semi-arid countries such as South Africa, with highly variable rainfall regimes (Johnston et al. ), in part associated with El Niño events, which typically bring about below-average rainfall conditions and drought (Nicholson & Kim ).
There are, however, constraints to the use and benefits of seasonal forecasts in agriculture, often between endusers and producers. These include credibility (i.e., perceived technical quality and authority of information), salience (i.e., the utility of information and perceived relevance to users' needs), legitimacy (i.e., perception that the forecast producers seek the users' interests) and understand- While seasonal forecasts are generally applied to rainfed agriculture (Johnston ), this paper rather considers their potential as a tool for medium-term (seasons to years) management of heavily exploited shallow aquifers in South Africa, where groundwater is critical for irrigation and seasonal forecasts are produced nationally and downscaled for provincial use.

Aims
This paper examines groundwater management in the farming town of Dendron (now formally known as 'Mogwadi' for political reasons, after a country-wide shift away from Afrikaans-named towns) in the Limpopo River Basin in South Africa, and considers current and potential use of seasonal forecasts in long-term resource management and in the context of intensive use for agriculture. The linkages between climate variability and management strategies are explored for the benefit of agricultural groundwater use.
The contention is that with better knowledge and planning of groundwater replenishment as informed by seasonal forecasts, farmers could improve the formulation of their cropping and irrigation plans, and be better equipped to collectively manage their groundwater resources sustainably.  The remainder of this paper is structured as follows.
First, a review of the case study of Mogwadi (Dendron) and the methodology utilised is presented, followed by the results and discussion section, which examines management approaches and the utility of seasonal forecasts. Finally, the conclusions and recommendations drawn from the study are given.

Hydrogeological characteristics of the aquifer
The geology is characterised by crystalline (granite) complex of the Hout River Gneiss throughout the catchment. Geologically, the aquifer is broadly divided into an upper weathered aquifer and a lower fractured aquifer. According to Jolly (), the lower zone is high-yielding, while the upper weathered formation is low-yielding with low storage.
The fractured aquifer represents the zone screened by most production wells in the area. Dolerite dikes cut across the greater area in various directions (Busari ), as seen locally in Figure 1   Groundwater abstraction concurrently increased from 9.2 × 10 6 m 3 yr À1 to 21.7 × 10 6 m 3 yr À1 , while groundwater levels were estimated to have decreased from 18 m to 43 m below ground level (i.e., a 25 m drop) (Abtmaier ; Dziembowski ; Jolly ). Comparing abstraction data with the long-term recharge estimates above indicates a negative water balance for the area. influenced mostly by differences in pumping patterns and geology. Monitoring well A7N0019 is from a sandy aquifer adjacent to the river, while A7N0524 is from the hard rock aquifer further from the river. The response to rainfall events is therefore much more subdued in the latter due to the deeper depth of the water table. Well A7N0019 is influenced by its proximity to the river, presumably entailing additional focused recharge and hence a quicker and more pronounced response. The general trend described above of groundwater level declines in the hard rock areas from the 1960s to 2000 is also seen in A7N0524. It is also clearly apparent that the exceptionally wet year of 2000which generated flooding in large parts of the Limpopo Basinhelped replenish the aquifer substantially in a relatively  short period. This indicates a multi-year pattern of groundwater depletion and rainfall-induced recovery in the area, and further illustrates the importance of having continuous information on groundwater levels and the potential role of forecasting information of rainfall in agricultural groundwater use. It is also important to note that while these wells are not pumped, they could be influenced by nearby groundwater abstraction, as often the monitoring wells are located close to intensive use areas (Verster , personal communication).
In the 1980s, work was carried out to determine the 'safe yield' of the aquifers in Mogwadi (Dendron). Jolly () states that the 'safe yield' for the aquifer is 8.6 × 10 6 m 3 yr À1 , based on a constant fraction (approximately 4%) of the annual rainfall, which roughly equates to estimated recharge rates (Masiyandima et al. ). However, the usefulness of the 'safe yield' concept is heavily debated in the literature, with several authors noting that a fixed yield is not an operational rule that works under all climatic conditions, and that yields vary over time alongside environmental conditions (Sophocleous ; Loáiciga ; Jarvis ). This is particularly important in environmental conditions such as those experienced in Mogwadi (Dendron), where rainfall, and therefore recharge of shallow aquifers, vary significantly between wet and dry seasons, and between years.
Furthermore, Pierce et al. () argue that a single number is insufficient in guiding groundwater management and policy. Therefore, the physical science component of the safe yield concept can be integrated with the consensus yield conceptderived from stakeholders' preferencesinto an aquifer-yield continuum (Pierce et al. ). Such an approach ensures that any management strategy conceived can withstand social pressures, while also being technically feasible (Pierce et al. ). This study therefore takes a step toward a more integrated approach to groundwater management that not only considers science-based approaches, such as seasonal forecasts and monitoring data, but also community engagement and the socio-political realities of a local situation.

Climate variability and groundwater
In resource governance, users' perceptions of the physical situation is important for analysing resource management decisions. Interviews and workshops conducted highlighted varied understanding among farmers regarding the relationship between climate variability and groundwater levels, although most felt that seasonal climate variability and long-term climate change pose a threat to groundwater resources and play an important role in management. This was mainly due to the fact that groundwater in the area is observed to depend predominantly on episodic rainfall events, either as diffuse or focused recharge alongside the Hout River (which flows for only 2-3 weeks per year) and the confluent Sand River. Most interviewees agreed that groundwater levels in the hard rock areas only respond to high rainfall periods (typically above 250-300 mm over three months). However, this is also affected by factors such as local geology, slope and surface land use. Drought events impact groundwater in the area at a much slower rate, although a DWS hydrogeologist interviewed asserted that drought is felt sooner in Mogwadi (Dendron) than surrounding areas due to higher abstraction rates.
Most interviewees had noticed changes in climate behaviour in the past ten years. Perceptions included increasing average annual temperatures, more extreme temperature differences between summer and winter, and shifting seasons (e.g., delays in the arrival of the rainy season). Interviewees reported varied experiences regarding changes in groundwater levels; several commented that they had seen widespread depletion over the past ten years, while two interviewees stated that levels in some areas were, in fact, increasing due to better borehole management. Table 1 identifies key years and climatic events as remembered by the sample of farmers.

Groundwater management system
Numerous strategies for groundwater management are car-     Minister for the Limpopo Province that the agricultural sector would be having its water allocations re-assessed due to 'water wastage'. The consensus among interviewed farmers was that the government's focus is wrongly on the economic value of water, favours the mining industry's needs over the agricultural sector, and has a consequent lack of concern for rural livelihoods and local food security.

Informal management effectiveness
Informal management strategies were perceived to be much more effective than formal management, rated at 70% effectiveness by interviewees. This was due to a high level of coordination between farmers, alongside individual actionsalthough in many cases, these successes were self-proclaimed.
One approach taken is a 'gentlemen's agreement', whereby boreholes on farms are drilled at a minimum distance of 50-100 m from farm borders to ensure that farmers' abstraction activities do not impact neighbouring farms, which one farmer claimed 'reduces [the risk of] conflict between farmers'. Sixty per cent of farmers also claimed to irrigate during the night when evapotranspiration is low, thus reducing water consumption. However, this strategy may be undertaken primarily due to cheaper electricity rates during off-peak hours, rather than concern for groundwater levels, and has not yet been verified. Three   Farmers tended to use short-term weekly weather forecasts for decision-making, alongside present climate and groundwater levels, rather than anticipatory predictions.
There was a high level of mistrust in the SAWS forecasts - Results also showed that farmers in Mogwadi (Dendron) preferred email and cell phone dissemination methods, and 80% of interviewees felt forecasting information would only be beneficial if shared well in advance of the rainy season (i.e., around September). Much of this is beyond the current level of forecast ability, particularly the request for intraseasonal rainfall. Forecasts may therefore also have to be developed to cater for groundwater use by including groundwater level datafor example, by combining climate forecasts with the quarterly reports compiled by DWS. An 'ideal forecast' is characterised in Table 4.

CONCLUSIONS
This paper has presented the case study of Mogwadi (Dendron), Limpopo, and its ongoing issues surrounding groundwater management. The study examined current understanding across main stakeholders in the study area regarding groundwater dynamics and management strategies, and then assessed the potential utility of seasonal climate forecasts within this context.
It was found that limited forecasting information is available for commercial farmers in the area, which is not fully utilised due to issues of saliency, legitimacy, credibility and understanding of the forecasts. A key constraint was limited communication between forecast producers, DWS and farmers. It was also found that the lack of use of forecasting information was related to poor understanding of the information provided and unclear linkages to groundwater management. There was interest in future use of forecasts, if tailored for farmers' needs (interest was stimulated by an intervening drought between separate consultations).
Mogwadi (Dendron) is a particularly interesting and important case study of a water user group trapped in a prisoner's dilemma, with a lack of regulation coupled with increasing socio-economic and environmental pressures.