Exploring the Potential of LPJmL-5 to Simulate Vegetation Responses to (Multi-Year) Droughts

Abstract. Climate change is expected to increase the frequency and severity of Multi-Year Droughts (MYDs), but their impacts on vegetation remain poorly understood. While satellite records offer valuable insights, they cover only recent decades, limiting the number of MYDs available for analysis. Dynamic global vegetation models (DGVMs), such as LPJmL-5, can help overcome this limitation by simulating vegetation dynamics over longer timescales. However, their ability to capture drought impacts has not yet been systematically evaluated. In this study, we benchmark LPJmL-5 against MODIS-derived gross primary production (GPP) to assess how well it captures vegetation responses to drought. We find that LPJmL-5 reproduces GPP reasonably well in some regions, but improvements can still be made in the Southern Hemisphere and for croplands. During MYDs, LPJmL-5 captures the key temporal and spatial GPP drought dynamics observed in MODIS. However, the model tends to overestimate vegetation response at the onset of MYDs and shows some rapid recovery behaviour, resulting in muted overall drought impacts. Vegetation responses also vary by type: croplands show relatively good agreement, while boreal and temperate vegetation underestimate positive and negative impacts, respectively. These discrepancies appear to be linked to simplified model representations of vegetation stress and mortality, which limit long-term vegetation loss. Our results highlight the need to improve how LPJmL-5 simulates vegetation stress and recovery, especially under prolonged drought conditions, in order to better capture ecosystem vulnerability in a changing climate.