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Resilience and Adaptation in Drylands. Identifying past water management practices for drought-resistant crops

Periodic Reporting for period 4 - RAINDROPS (Resilience and Adaptation in Drylands. Identifying past water management practices for drought-resistant crops)

Reporting period: 2022-07-01 to 2023-12-31

RAINDROPS aimed to offer a comprehensive perspective on human adaptation to, and the establishment of resilient cultivation systems in drylands. These areas constitute over 40% of the Earth's surface and are inhabited by approximately 2.3 billion people. In these regions, cultivation often relies on irrigation, a permanent water source, or various rainwater harvesting techniques. Despite this, there are instances of successful rain-fed cultivation systems, even in hyper-arid locations. Archaeologically, studying different levels of crop water management, particularly rain-fed cultivation, poses significant challenges due to the lack of reliable proxies for these practices. A potential solution lies in determining water availability directly from archaeobotanical material, specifically ubiquitous and well-preserved micro-remains like phytoliths.

To achieve its goals, RAINDROPS integrated research on plant physiology with original archaeobotanical applications and records of Traditional Ecological Knowledge (TEK) of the cultivation of three major tropical and sub-tropical crops: pearl millet (Pennisetum glaucum), finger millet (Eleusine coracana), and sorghum (Sorghum bicolor). RAINDROPS combined experimentally controlled data of macro-remains (stable carbon and nitrogen isotopes of grains) and micro-remains (phytolith morphological ratios, stable oxygen, and silicon isotopes from phytoliths) with ethnographic evidence to create a methodological framework for assessing crop water availability in the past.

The main results of the project indicated that finger millet, pearl millet and sorghum, can be cultivated rainfed in areas that receive much less annual rainfall than previously considered viable. Some of these crops have been an important part of the diet of people inhabiting dry sub-humid areas of Northern Ethiopia where they might have been cultivated without irrigation since prehistory. Overall, the combined modelling of different archaeobotanical proxies can provide valuable information on past water management practices in drylands and allow reconstructing long-term occupation of such areas of the world. This in turns, provides a different view on the role of arid areas, and the possible mechanisms to increase human adaptation to drylands in the future.
Throughout the project, we conducted a series of activities to explore long-term cultivation practices of the three C4 species under study: we conducted experimental cultivation under controlled conditions, we performed ethnoarchaeological interviews with local traditional farmers, we modelled ethnoarchaeological data and applied these models to archaeological evidence, and we performed archaeobotanical analysis of millets from selected sites.

Three seasons of experimental cultivation were carried out, two at ICRISAT (Patancheru, Hyderabad, Telangana, India), and one at Universitat Pompeu Fabra (Barcelona, Spain) using an approach that enabled precise control over watering conditions for plants grown under different regimes, facilitating the study of their responses to water treatments and their transpiration rates. The data collected provided insights into the relationship between plant watering and the archaeological proxies under investigation. The analysis included carbon and nitrogen stable isotopes composition of grains (fresh and charred), total biosilica extracted from plant tissues, phytolith morphotypes abundance and ratio, and stable oxygen and stable silicon isotopic composition of phytoliths. Results were modeled and used to examine watering practices in samples from the Indus Civilisation (Sindh, Pakistan) and Pre-Aksumite and Aksumite contexts (Tigrai, NE Ethiopia) and neolithic contexts (Central Sudan).

Ethnographical interviews with local farmers were conducted in Pakistan, Ethiopia, and Sudan. In Pakistan, we explored an area near the Khirtar mountains in Sindh, where farmers cultivate rain-fed sorghum and pearl millet. In Ethiopia we collaborated with sorghum and finger millet farmers in Tigrai. Additionally, in Sudan, we interviewed farmers cultivating rain-fed pearl millet and décrue sorghum in the Khartoum State. The ethnographic work revealed similarities in decision-making processes among farmers dealing with scarce and unpredictable rainfall, as well as specific adaptations unique to each region. This information allowed us to construct a global model of the cultivation of three specific crops (pearl millet, finger millet, and sorghum) by combining a cross-cultural approach with the data collected during interviews.

Finally, we analyzed samples of phytoliths and seeds from several archaeological sites in drylands, primarily in Pakistan, Sudan, and Ethiopia, but also in Egypt and South Africa. The integration of data and models developed in the experimental and ethnographic work packages enabled us to reconstruct water management practices and land-use strategies associated with millet cultivations at these archaeological sites.
Pre-industrial agriculture in drylands has often been regarded as a secondary activity, feasible only in regions with consistent and secure water sources. However, it is evident that past human groups experimented with a diverse array of crops, some well-adapted to water-constrained areas, such as millets. These crops now represent crucial sources for future biodiverse and sustainable agriculture worldwide. Drylands agriculture has gained prominence in development studies due to desertification's impact on food security for a substantial portion of the global population. Although the potential of archaeology to inform long-term human adaptation strategies is widely acknowledged, archaeobotanical studies have been underutilized in addressing modern issues.

RAINDROPS integrated crop physiology, traditional ecological knowledge, and archaeobotanical research on a broad scale to study drylands crops in a long-term perspective. Collaborations with institutions like the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT) positions the project's outcomes at the forefront of drylands crop research, with the potential to influence local and international policies on sustainable development in these regions. Our work on local crops, utilizing published maps, data, and field studies, has revealed a variety of cultivations not reported in official land-use maps (e.g. Harvest Choice or FAO); it indicated that annual rainfall is not a reliable parameter to assess agricultural potential of arid areas; and it has underscored that Traditional Ecological Knowledge (TEK) is a valuable source of information on agricultural practices and local adaptations to the environment and climate, often overlooked or underutilized by institutions.

Indeed, fieldwork has brought to light local cultivation practices even in areas traditionally deemed inactive or dedicated to monocropping, challenging current observational biases on present and past agricultural practices in drylands. The application of the knowledge gained by experimental and ethnoarchaeological work, modelled quantitatively, has allowed the formulation of hypotheses on past water management practices in different prehistoric and early historic contexts, pushing the cultivation of drought-resistant rainfed crops back by several centuries.
Ethnoarchaeological work in Tigray, Ethiopia
Silicon stable isotope analysis on phytoliths, GFZ, Potsdam, Germany
Pearl millet field in Sudan