Significance Increasing diversity within crops may be a powerful way to reduce agricultural declines from climate change. As such, it has garnered increasing attention, especially in documenting within-crop diversity through different cultivars or wild relatives. Yet, there are few tests of whether this diversity can mitigate losses with warming. Here, using European (predominantly French) databases to forecast winegrape phenology, we test if shifting cultivars changes predictions of future growing regions. We find that cultivar diversity halved potential losses of winegrowing regions under a 2 °C warming scenario and could reduce losses by a third if warming reaches 4 °C. Thus, diversity—if adopted by growers locally—can mitigate agricultural losses, but its effectiveness will depend on global decisions regarding future emissions.

Abstract Agrobiodiversity—the variation within agricultural plants, animals, and practices—is often suggested as a way to mitigate the negative impacts of climate change on crops [S. A. Wood et al., Trends Ecol. Evol. 30, 531–539 (2015)]. Recently, increasing research and attention has focused on exploiting the intraspecific genetic variation within a crop [Hajjar et al., Agric. Ecosyst. Environ. 123, 261–270 (2008)], despite few relevant tests of how this diversity modifies agricultural forecasts. Here, we quantify how intraspecific diversity, via cultivars, changes global projections of growing areas. We focus on a crop that spans diverse climates, has the necessary records, and is clearly impacted by climate change: winegrapes (predominantly Vitis vinifera subspecies vinifera). We draw on long-term French records to extrapolate globally for 11 cultivars (varieties) with high diversity in a key trait for climate change adaptation—phenology. We compared scenarios where growers shift to more climatically suitable cultivars as the climate warms or do not change cultivars. We find that cultivar diversity more than halved projected losses of current winegrowing areas under a 2 °C warming scenario, decreasing areas lost from 56 to 24%. These benefits are more muted at higher warming scenarios, reducing areas lost by a third at 4 °C (85% versus 58%). Our results support the potential of in situ shifting of cultivars to adapt agriculture to climate change—including in major winegrowing regions—as long as efforts to avoid higher warming scenarios are successful.

The potential adverse effects of climate change on agriculture, including shifts in growing areas, decreased yields, and crop failures (1⇓⇓⇓⇓–6), are a major concern to practitioners, policymakers, scientists, and consumers alike (7). Forecasts predict a future where regional climates will become increasingly mismatched with crops currently cultivated in those regions (e.g., ref. 8), unless there are large shifts in agricultural practices.

Practices that increase the resilience of agricultural regions would foster growing regions that can maintain normal processes and function—including in yields and quality—despite increases in stress or disturbance (9) from climate change. Research has especially focused on exploiting intraspecific crop diversity (10⇓⇓⇓⇓–15) because of its potential to increase resilience without requiring agricultural regions or the crops they grow to shift. As expansion of agriculture is one of the primary drivers of biodiversity loss, keeping agricultural regions in place and thereby preventing natural lands from being lost to new agricultural regions is a major international conservation goal (16, 17).

To increase resilience with climate change, intraspecific diversity must link to the traits most needed to adapt to future climate regimes (2). Such traits include a cultivar’s heat and drought tolerance and its phenology—the timing of recurring developmental stages, such as budburst and maturity. Variation in phenology may be a particularly important trait for developing agricultural systems resilient to climate change, as differences in cultivar phenology (e.g., an early versus late-ripening cultivar) can translate to very different climatic conditions during critical developmental phases, such as fruit maturation.

Given enough variation in traits—such as phenology—across cultivars, growers could select and plant cultivars suited to their current climate, then shift to more appropriate cultivars over time as the climate shifts, a process we refer to as “turnover.” Cultivar turnover is expected to increase the resilience of agricultural systems and thus lead to improved agricultural forecasts (18). Yet, this basic assumption, which underlies much of the current research, has rarely been tested.

Here, focusing on winegrapes (Vitis vinifera subspecies vinifera), we quantify how much in situ cultivar turnover affects forecasts of suitable growing regions with climate change. We selected winegrapes, given their high diversity and extensive records, which make testing the importance of intraspecific diversity to forecasts possible. Growers today plant over 1,100 different vinifera cultivars of winegrapes (19), called varieties, which are geographically and morphologically diverse. Different varieties possess important trait variation related to climate, including variation in phenology of 6 to 10 wk across varieties grown in the same climate (20).

Winegrape diversity is well documented, allowing us to combine winegrape phenology and global variety-level planting data with projections of daily temperature and precipitation from a large ensemble of a state-of-the-art climate model (Community Earth System Model [CESM]; SI Appendix, Fig. S5; ref. 21) to forecast climatic suitability of 11 globally planted varieties of winegrapes (Cabernet-Sauvignon, Chasselas, Chardonnay, Grenache, Merlot, Monastrell [synonym Mourvèdre], Pinot noir, Riesling, Sauvignon blanc, Syrah, and Ugni blanc). These varieties make up 35% of the area planted globally, reaching 64 to 87% in many important winegrowing countries (e.g., Australia, Chile, France, New Zealand, Switzerland, and the United States; ref. 22).

Our approach to model future winegrowing regions provides an important advance on previous efforts. Studies to date have generally ignored intraspecific diversity (forecasting only one or few varieties) and have used species-distribution models or simple linear phenological models, which fail to adequately include nonlinear developmental responses to temperature (23). Instead, our approach fits nonlinear process-based models for multiple varieties, which can predict expected phenological delays due to heat stress, and characterizes specific climatic conditions during maturation. Using predominantly French long-term phenology records (SI Appendix, Tables S1 and S2), we developed and validated models to forecast budbreak, flowering, and the onset of ripening (veraison) in each region for two warming scenarios, +2 °C and +4 °C, and a 0 °C reference scenario of no warming (SI Appendix, Fig. S5; see also Warming Scenarios for more details). Next, using global data on winegrape variety plantings (22), we predicted the climatic suitability of each region during the ensuing maturation stage—a period that controls whether a variety can be harvested in a particular region each year (24⇓–26)—for our reference and warming scenarios.

To quantify the change (including gains and losses) in areas suitable for winegrowing, and resulting cultivar turnover, we compare our results relative to: 1) current winegrowing regions, and 2) areas identified as climatically suitable (estimated as supporting at least one of the 11 cultivars modeled to maturity in most model years) under our 0 °C reference scenario (Calculating Climatic Suitability).

Discussion Our results show that cultivar diversity can decrease the loss of agricultural areas by over 50%—highlighting the critical role that human decisions play in building agricultural systems resilient to climate change. We show that cultivar turnover—if adopted by growers locally—can reduce the negative outcomes of climate change on winegrapes, with implications for other crops with high diversity. However, we also find that the benefits of cultivar turnover decline under greater warming. Without global efforts to reduce emissions sufficiently to stabilize temperatures at or below 2 °C, our results suggest that half of current global winegrowing regions would become climatically unsuitable for today’s major winegrapes. These findings do not extend to all regions—in some regions, we find that cultivar diversity alone may not be enough to prevent declines. As seen in other studies (e.g., ref. 16), gains and losses of varieties are distributed unequally across the globe (Fig. 1), with warmer regions suffering the greatest losses and cooler regions seeing higher gains. Currently, even if growers exploit cultivar diversity, top-producing countries, particularly in Southern Europe, are predicted to sustain major declines of suitable winegrowing areas, with minimal gains (Fig. 1 C and D). For example, Spain and Italy are expected to lose 65% and 68%, respectively, of climatically suitable areas, under a 2 °C warming scenario (SI Appendix, Fig. S15), with gains of only 5% and 9% (respectively). France is projected to see balanced losses (22%) and gains (25%; SI Appendix, Fig. S15). In contrast, wine-producing regions in the Pacific Northwest (United States) or New Zealand expand in climatically suitable area for the latest-ripening varieties by 20 to 100% and 15 to 60%, respectively (SI Appendix, Fig. S15). Further, losses increase dramatically under a 4 °C warming scenario (SI Appendix and Figs. 1d and 2), while gains decrease. Losses at 4 °C are predicted to be particularly high in countries that are already warm; this includes losses reaching ∼90% in Spain and Italy (SI Appendix, Fig. S15). For regions where our results suggest that cultivar diversity may be most critical, growers must choose to actively shift varieties—which requires overcoming legal and cultural hurdles. Currently, traditional practices, alongside regulations at local, regional, and higher levels, limit how much and where growers can shift varieties easily (19). This, coupled with other considerations, such as the temporal and related financial cost of replanting or regrafting a vineyard, may lead many growers to prefer alternative options that keep a particular variety tied to a region. For example, local management practices to reduce microclimatic temperatures or adjust the pace of development (e.g., shade cloth, reduced leaf area to fruit weight ratio, or longer-cycle rootstocks)—may help some growers (30⇓–32), but generally work best for lower amounts of warming, especially compared to changing varieties. Growers who want to exploit cultivar diversity would benefit from improved climate and crop-diversity data. For winegrapes, an immediate need is data on a greater number of varieties at a vineyard-relevant spatial scale. Our modeling approach requires projected climatic data at a high temporal resolution (e.g., simulated daily temperature values), which are only available at a low spatial resolution (e.g., circa 100 k m 2 pixels), and thus cannot capture the unique microclimates of many vineyards. Our results could be expanded to finer spatial resolutions, given climate data downscaled with attention to the important climatic attributes of a particular viticultural region (e.g., coastal influences and/or cold air pools in complex terrains). Additionally, our approach requires sufficient phenological data, which we obtained for 11 varieties from a narrow geographical range (i.e., mainly France). These varieties span a diversity of phenologies (SI Appendix, Figs. S4 and S14E), yet they still represent less than 1% of known winegrape diversity, suggesting that benefits from cultivar diversity could be higher if more varieties were included. Our results apply clearly to winegrowing regions, but have implications for many of the world’s agricultural regions. We focused on winegrapes given their diversity and extensive data resources: winegrape harvest dates are some of the longest written records on earth (33); major repositories collect, preserve, and document the crop’s diversity (20); and newly available data describe the planted geographic distribution of winegrape varieties across the globe (22). Such resources make winegrapes an excellent crop to test how intraspecific diversity may help agriculture adapt to a changing future, but many other crops also harbor high genotypic and phenotypic (e.g., morphological) diversity. Some of this diversity is obvious to consumers (e.g., historical and new cultivars of apples; ref. 13), while other diversity is hidden, present mainly in the wild or in research collections (e.g., banana and orange; refs. 34 and 35, respectively). Gathering sufficient data for tests similar to ours will be critical to identifying the full potential of cultivar turnover, but we expect that our results extend to many other crops, if growers have the flexibility and resources to shift in step with climate change.

Acknowledgments We thank C. Marchal and S. Dedet, who helped with data from the Institut National de la Recherche Agronomique Domaine de Vassal Grape Repository; T. J. Davies, A. K. Ettinger, and two anonymous reviewers for comments that improved the manuscript; and all those who shared data. We thank Harvard Research Computing for computing facilities. I.M.-C. acknowledges funding from a postdoctoral fellowship by University of Alcalá and from the Spanish Ministry of Science and Innovation (Grant CGL2017-86926-P to M. Á. Rodríguez).

Footnotes Author contributions: I.M.-C., I.G.d.C.-A., B.I.C., T.L., A.P., C.v.L., K.A.N., and E.M.W. designed research; I.M.-C. and E.M.W. performed research; I.M.-C., I.G.d.C.-A., and E.M.W. analyzed data; I.M.-C. and E.M.W. wrote the paper; I.M.-C., I.G.d.C.-A., B.I.C., T.L., A.P., C.v.L., K.A.N., and E.M.W. contributed ideas; I.M.-C., I.G.d.C.-A., B.I.C., T.L., A.P., C.v.L., K.A.N., and E.M.W. edited the manuscript; I.M.-C. designed and produced the figures; I.G.d.C.-A., B.I.C., and A.P. contributed to the writing of supporting information; and A.P. built the database.

The authors declare no competing interest.

This article is a PNAS Direct Submission.

Data deposition: Analyses other than phenological parameterization and cross-validation utilized custom computer R code, freely available at GitHub, https://github.com/MoralesCastilla/PhenoDiversity.

This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1906731117/-/DCSupplemental.