DPLUS051 Water Security and Sustainable Cloud Forest Restoration

The project has been a collaboration between SHG, Connect Saint Helena, Centre for Ecology and Hydrology and Arctium. Further support was provided by RBG Kew and SHNT. The islands 20-Year Water Resource Masterplan outlined development and management of island water resources to provide security of supply and enable resilience to climate change. The preferred development approach being through rainwater harvesting (mist capture).

This Darwin Plus funded study was completed to prove or disprove the following hypothesis:

Improving mist capture in the Peaks national park through restoring endemic cloud forest would increase available water resources and provide more cloud forest habitat for at risk endemic plants and invertebrates.

The project’s research in Wells Gut and Grapevine Gut has identified important areas which could affect the future resilience of the Island and water security. Data shows that water supplies can be improved through cloud forest restoration, as mist captured by vegetation in the Peaks provides more water over a year than through normal rainfall. This has the added advantage of increasing the area of habitat needed to safeguard the islands endemic invertebrates and cloud forest plants.

Below are key facts which are included into the project report:

  • The study area provides 38% of the islands water supply;
  • Mist comprises over 60% of precipitation (mist + rainfall) during the year and is the main source of precipitation for the island during the summer months;
  • Rainfall recorded at Grapevine Gut is 3.9 times higher than at Bottom Woods Met Station in 2017;
  • Mist forms at a higher elevation on the windward (south east) side of the Peaks in Perkins Gut than on the leeward side in Wells Gut;
  • The minimum height above sea level that mist forms is 690mASL;
  • Stream flows as a proportion of each water balance vary significantly between Wells Gut and Grapevine Gut indicating that the relationship between sub-catchment geology, soils, rainfall recharge, dry weather flow and spring flows is the key to understanding how water reaches the streams from mist and rainfall;
  • The use of drones for aerial photography was successful and demonstrated that this technology can enhance conservation work as the data can be used to map vegetation, water catchments, measure the success of invasive species removal and cloud forest restoration programmes, reduce health and safety risks associated with remote field work, plan conservation work and assess changes in habitat over time;
  • The way the island receives its water is going to change due to climate change. The number and distribution of wet and dry days will change along with rainfall intensity;
  • Rainfall is predicted to fluctuate between -2.50mm and +2.05mm per month by 2099, with the number of consecutive dry days increasing up to 48% on the present day. This increases the probability of the island experiencing more periods of drought;
  • Encouraging a larger area of cloud forest and developing a richer peaty subsoil in the Peaks will help even out the islands yearly water supply by slowing rainfall runoff and releasing water in a slower less “flashy” flow. Stream data show that it only takes 3 days for rainfall to reach the streams in the Peaks, limiting the time that water stays within the catchments; and
  • Data suggest that endemic native habitats are potentially more resilient to climate change than the introduced vegetation. The climate change assessment identified altitudinal shifts in the vegetation zone as being critical for the endemic plants and invertebrates within Grapevine Gut and Wells Gut, as a shift in the vegetation zone could significantly reduce the size of the cloud forest.

Outcomes of the project report have been used to support the drafting of the Peaks Management Plan.