Implementing climate change projections in System Dynamics models

Desertification is the degradation of drylands, which occupy an increasing proportion of the Earth's surface due to global warming. It is currently the most extensive biome on Earth, occupying 45% and one out of every three inhabitants of the planet live in them. One of the most effective ways to face desertification, as Land Degradation Neutrality points out, is prevention. For this purpose, simulation models are very useful tools. Specifically, System Dynamics models are particularly effective, since they allow bringing together the biophysical and socioeconomic variables involved in the formation of the problem. These integrative models, coupled with other tools such as sensitivity analyses, are used to generate desertification early warning indicators. The objective of this programming routine is to implement climate change scenarios in these simulation models. The script presented here was used to evaluate the sensitivity of dehesa rangelands productivity to the increase in the frequency and intensity of droughts due to climate change. • Integrated simulation models are useful tools to understand complex socioecosystems. • Land-use changes foster the alteration of key hydro-bio-geochemical processes. • By means of automated import processes and data analysis programming, it is possible to implement desertification early warning systems.This work was supported by the funded by the European Research Council [grant agreement n°647038 (BIODESERT)]; Ministerio de Ciencia e Innovación de España (Spain), through European Regional Development Fund (FEDER) [SUMHAL, LIFEWATCH-2019-09-CSIC-13, POPE 2014-2020]

System Dynamics Tools to Study Mediterranean Rangeland’s Sustainability

Rangelands are a key resource present all over the world and cover half of all emerged lands. They are even more important in drylands, where they cover 48% of the total area. Their intensification and the additional pressure added by climate change push these socio-ecological systems towards desertification. Over the last two decades, we have developed and applied System Dynamics (SD) models for the study of Mediterranean grasslands. In addition, we have designed procedures and analysis tools, such as global sensitivity analysis, stability analysis condition, or risk analysis, to detect the main drivers of these socio-ecological systems and provide indicators about their long-term sustainability. This paper reviews these works, their scientific background, and the most relevant conclusions, including purely technical and rangeland-related ones, as well as our experience as systemic modelers in a world driven by field specialists.This research was funded by DeSurvey (CE-Integrated Project Contract No. 003950), PADEG (CGL2008/01215/BTE), and BIODESERT (European Research Council grant agreement No. 647038)

What is desertification, and why do we have to tackle this problem?

La desertificación se refiere a la degradación de las tierras secas, que ocupan el 45% de la superficie terrestre y en ellas vive una de cada tres personas. Unos mil millones de personas, en los países más pobres, dependen de la tierra para la mayoría de sus necesidades. La desertificación es consecuencia de las variaciones climáticas –como las sequías– agravadas por el cambio climático, y las actividades humanas, que suponen intensificar el uso del suelo para cubrir las necesidades de una población y consumo per cápita crecientes. Las trabas conceptuales, la falta de soporte científico y la doble visión de la Convención de Naciones Unidas de Lucha contra la Desertificación (CNULD) –ambientalista vs desarrollista– ha lastrado la implementación de soluciones. Para revertir esta situación es necesario comprender que los mismos factores que generan riqueza son los causantes de la desertificación. Degradación y regeneración son procesos que conviven y que deben formar parte del mismo paquete de soluciones, como reconoce el concepto de degradación neutra (NDT). Esta es la iniciativa de la CNULD para lograr la neutralidad en la degradación de tierras en 2030. Para ello, además de las restauraciones ecológicas, debe priorizarse la prevención y un uso del territorio que minimice los impactos ambientales. La NDT forma parte del ODS 15, pero abordar la desertificación pasa por lograr otros ODS, destacando el de la igualdad de género (ODS 5), el hambre cero (ODS 1) o el fin de la pobreza (ODS 2). Solo con un mundo más justo puede lograrse un planeta sostenible.Desertification refers to the degradation of drylands, which cover 45% of the earth’s land surface and are home to one in three people. Some one billion people in the poorest countries depend on the land for most of their needs. Desertification is a consequence of climate variations such as droughts, aggravated by climate change and human activities, which involve intensifying land use to meet the needs of a growing population and per capita consumption. Conceptual obstacles, lack of scientific support and the double vision (environmentalist vs. developmentalist) of the United Nations Convention to Combat Desertification (UNCCD) have hindered the implementation of efficient solutions. To reverse this situation, it is necessary to understand that the same factors that generate wealth are the causes of desertification. Degradation and regeneration are processes that coexist and must be part of the same solution package, as recognized by the concept of land degradation neutrality (LDN), which the UNCCD aims to achieve by 2030. To this end, in addition to ecological restoration, priority should be given to prevention and land use that minimizes environmental impacts. LDN is part of Sustainable Development Goal 15, but tackling desertification involves achieving other SDGs, such as gender equality (SDG 5), zero hunger (SDG 1) and the end of poverty (SDG 2). A sustainable planet can only be achieved with a fairer world.Este trabajo ha sido financiado por el Consejo Europeo de Investigación (Grant Agreement nº 647038, BIODESERT)

Estudio de la desertificación por sobrepastoreo mediante un modelo de simulación dinámica

En esta tesis doctoral se presenta un modelo de simulación dinámica, denominado DESPAS, cuyo fin es contribuir al entendimiento de los sistemas ganado-pasto-suelo, en general, y de los procesos de desertificación por sobrepastoreo, en particular. Dos son las principales características novedosas del modelo: (i) el tratamiento conjunto de los tres elementos citados; y (ii) la consideración de una dinámica del ganado determinada directamente por variables de tipo económico. Con la construcción y el análisis de DESPAS pretendemos contribuir a algunas de las propuestas hechas por el Programa de Acción Nacional contra la Desertificación (PAND), que tienen que ver con el llamativo déficit científico que sobre el tema existe en España, uno de los países europeos con mayores problemas de desertificación. Así, este trabajo estudia cuáles pueden ser las manifestaciones de uno de los escenarios posibles de desertificación en nuestro país, el sobrepastoreo, y propone el cálculo de ciertos indicadores para evaluar el riesgo de que ocurra dicha desertificación a largo plazo. El análisis de las manifestaciones posibles del proceso de desertificación por sobrepastoreo, es decit, el estudio de los comportamientos dinámicos posibles de DESPAS, ha mostrado las significativas diferencias que se dan entre considerar un subsistema ganado-pasto aislado, como la literatura ha venido haciendo habitualmente hasta la fecha, y considerar de forma conjunta un sistema ganado-pasto-suelo. Por su parte, los indicadores de desertificación propuestos tienen la virtud de poner en relación parámetros físicos y ecológicos con otros de tipo técnico y económico. Dichos indicadores han sido aplicados a tres escenarios ideales, aunque verosímiles: vacuno en dehesa extremeña, ovino en dehesa extremeña y caprino en pastizales montañosos del sudeste; Esta aplicación ha venido a confirmar el riesgo de desertificación de la dehesa, anunciado por el PAND, y ha mostrado la extrema sensibilidad del citado sistema de producción caprina. Finalmente, esta tesis ha pretendido resaltar cuáles son los aspectos relacionados con el problema objeto de estadio sobre los que resulta más urgente reducir el déficit de conocimiento existente en nuestro país

SAT: A Software for Assessing the Risk of Desertification in Spain

Desertification is a major global environmental issue exacerbated by climate change. Strategies to combat desertification include prevention which seeks to reverse the process before the system reaches the stable desertified state. One of these initiatives is to implement early warning tools. This paper presents SAT (the Spanish acronym for Early Warning System), a decision support system (DSS), for assessing the risk of desertification in Spain, where 20% of the land has already been desertified and 1% is in active degradation. SAT relies on three versions of a Generic Desertification Model (GDM) that integrates economics and ecology under the predator-prey paradigm. The models have been programmed using Vensim, a type of software used to build and simulate System Dynamics (SD) models. Through Visual Basic programming, these models are operated from the Excel environment. In addition to the basic simulation exercises, specially designed tools have been coupled to assess the risk of desertification and determine the ranking of the most influential factors of the process. The users targeted by SAT are government land-use planners as well as desertification experts. SAT tool is implemented for five case studies, each one of them representing a desertification syndrome identified in Spain. Given the general nature of the tool and the fact that all United Nations Convention to Combat Desertification (UNCCD) signatory countries are committed to developing their National Plans to Combat Desertification (NPCD), SAT could be exported to regions threatened by desertification and expanded to cover more case studies.This work was funded by TRAGSATEC Public Enterprise on behalf of the Spanish Ministry of Agriculture, Food, and Environment under Contract 23.674. The generic desertification model was developed under the umbrella of DeSurvey IP (European Commission FP6 Contract no. 003950). The paper was written within the framework of the project BIODESERT, funded by the European Research Council (ERC Grant agreement no. 647038)

AQUACOAST: A Simulation Tool to Explore Coastal Groundwater and Irrigation Farming Interactions

In the framework of coastal groundwater-dependent irrigation agriculture, modelling becomes indispensable to know how this renewable resource responds to complex (usually not conceptualized nor monitored) biophysical, social, and economic interactions. Friendly user interfaces are essential to involve nonmodeling experts in exploiting and improving models. Decision support systems (DSS) are software systems that integrate models, databases, or other decision aids and package them in a way that decision makers can use. This paper addresses these two issues: firstly with the implementation of a System Dynamics (SD) model in Vensim software that considers the integration of hydrological, agronomic, and economic drivers and secondly with the design of a Venapp, push-button interfaces that allow users access to a Vensim model without going through the Vensim modelling environment. The prototype designed, the AQUACOAST tool, gives an idea of the possibilities of this type of models to identify and analyze the impact of apparently unrelated factors such as the prices of cultivated products, subsidies or exploitation costs on the advance of saltwater intrusion, and the great threat to coastal groundwater-dependent irrigation agriculture systems.This study was funded by the European Research Council grant agreement no. 647038 (BIODESERT)

Desertifying deserts

The current definition of desertification excludes hyper-arid zones given their lack of economic activity. However, the 101 million people living there, ongoing land degradation associated with the use of groundwater for intensive agriculture and climate-change-induced aridity call for a revision of this definition.This work was funded by the European Research Council grant agreement no. 647038 (BIODESERT). F.T.M. acknowledges support from Generalitat Valenciana (CIDEGENT/2018/041)

Life adapted to precariousness: The ecology of drylands

Drylands occupy approximately 40 % of the Earth's surface. Their peculiar hydrological regime, with water as the main limiting factor, together with other characteristics, such as the variability of rainfall and their ecological heterogeneity, turn these regions into one of the main and most relevant sets of biomes on the planet. Beyond their stereotypical conception as places with a low economic and ecological profile, these territories have enormous biodiversity and support 40 % of the world's population. Global warming is increasing atmospheric aridity and the strategies developed over millennia by their inhabitants are a model to learn from. Preserving these places is essential to combat climate change, and to do so, it is essential to have an in-depth understanding of their structure and functioning.This work was funded by the European Research Council (Grant Agreement Nº 647038, BIODESERT) and the Valencian Regional Government (CIDEGENT/2018/041). Emilio Guirado receives funding from the Regional Department of Education, Culture, and Sport of the Valencian Regional Government and the European Social Fund [project APOSTD/2021/188]

Unraveling Misunderstandings about Desertification: The Paradoxical Case of the Tabernas-Sorbas Basin in Southeast Spain

From its origins, the concept of desertification has been controversial. The prevailing confusion between two desertification visions, one that considers it as the expansion of deserts and another that emphasizes its anthropogenic component, has been transferred to society. Here we illustrate misunderstandings about desertification using a very illustrative case from the Tabernas-Sorbas Basin (Almeria, Spain), where striking badlands that are often used as an image of desertification coexist with an intensive olive agriculture that is irreversibly deteriorating the only oasis in continental Europe (Los Molinos spring). The olive tree is a traditional Mediterranean dryland crop and until the 1950s only about 200 ha were irrigated in this area. However, the profitability of the crop has caused irrigation to expand to 4400 ha in the last two decades. The process of intensification has been reinforced giving way to super-intensive irrigation, which involves going from 210 to 1550 trees/ha, which in a few years already occupies more than 1500 ha. The effects on the water balance of the aquifer feeding these crops have been severe, and the flow of the Los Molinos spring has gone from more than 40 L/s for the period 1970–2000 to the current 7.28 L/s. Unraveling the mechanisms of land degradation and its main drivers are the first step to propose management actions to achieve a more sustainable use of resources and to combat desertification.This research was funded by the European Research Council grant agreement nº 647038 (BIODESERT). FTM acknowledges support from Generalitat Valenciana (CIDEGENT/2018/041)

The Importance of Prevention in Tackling Desertification: An Approach to Anticipate Risks of Degradation in Coastal Aquifers

Groundwater degradation is a major issue on an increasingly hot and thirsty planet. The problem is critical in drylands, where recharge rates are low and groundwater is the only reliable resource in a context of water scarcity and stress. Aquifer depletion and contamination is a process of desertification. Land Degradation Neutrality is regarded as the main initiative to tackle land degradation and desertification. It is embedded in target 15.3 of the Sustainable Development Goals and focused on preventing these dynamics. Within this framework, we present an approach to assess risks of degradation and desertification in coastal basins with aquifers threatened by seawater intrusion. The approach utilizes an integrated system dynamics model representing the main relationships between the aquifer and an intensively irrigated area (greenhouses) driven by short- and medium-term profitability. The study area is located in a semi-arid region in Southern Spain, the Gualchos stream basin, which contains the Castell de Ferro aquifer. We found that the risk of salinization of the aquifer is 73%, while there is a 70% risk that the system would increases its demand for surface water in the future, and the chance of doubling the current demand is almost 50%. If the current system of reservoirs in the area were not able to satisfy such an increase in demand because of climate change, the basin would be at a serious risk of desertification.This research was funded by the European Research Council (ERC grant agreement 647038 (BIODESERT)) and by the project 101086497 funded by European Union’s Horizon-CL6-2022-Governance-01-07 research and innovation program