Adapting to climate change in Rerewhakaaitu A history of change at Rerewhakaaitu Background 400,000 years (at least) of volcanic activity, geological changes, and Lake Rerewhakaaitu lies within the climate changes Okataina Volcanic Centre where volcanic ca 17,600 years ago Volcanic activity and climate change eruptions have featured for at least the last 400,000 years (see Nairn, http: ca 800 years ago Maori settlement in New Zealand //www.gns.cri.nz/what/earthact/volcanoes/ 700 years ago Lake Rerewhakaaitu formed from the nzvolcanoes/okatbookprint.htm). Volcanic Kaharoa eruption of Mt Tarawera activity has been and will continue to be 140 years ago First recorded European settlement a huge factor in shaping the landscape, 120 years ago Most recent Tarawera eruption land use and water features in this area. Concurrently, past climate changes have 60 years ago Post-war farm ballots and development of Rerewhakaaitu also had a strong influence. Evidence of the end of the last glaciation and 40 years ago Local flooding and erosion problems onset of the current interglacial period The last 60 years Development (1950s and 60s), consolida- is found in the Rerewhakaaitu Tephra, tion (1970s), and progressive intensification arising from a Tarawara eruption about (1980s to present) of farming 18,000 – 17,400 years ago (Newham et The future ? al, 2003). PAGE • ADAPTING TO CLIMATE CHANGE IN EASTERN NZ Meso Adaptation Meso Adaptation ADAPTING TO CLIMATE CHANGE IN EASTERN NZ • PAGE 117 The most recent volcanic eruption, ‘Development experienced in the 1960s from Tarawera in 1886, has strongly of farming at and 1970s which is docu- influenced the present environment mented in correspondence at Rerewhakaaitu. There are three Rerewhakaaitu has from the time. These clearly defined soil zones in the occurred with deep- problems resulted from the area. Two were formed from the ening understanding combined effects of some 1886 eruption of Mt Tarawera and by farmers of both very wet years (experienced Lake Rotomahana, ash and mud soils the potential and in 1962, 1967, 1971) and the respectively. The third is an ash soil consolidation of farming in formed from earlier volcanic activity. limitations of their an area that was devoid of environment. Dominant tree cover as a result of the Lake Rerewhakaaitu is part of Te features are the 1886 eruption. The prin- Arawa’s historical holdings, with the cipal concern from farmers lakebed vested in Te Arawa along volcanic soils and the at the time was erosion with those of 12 other Rotorua lakes. presence of the lake.’ and degradation along The first significant human influence the upper reaches of the in the vicinity of Lake Rerewhakaaitu Mangaharekeke Stream. began in the 1860s. The area was This first became an issue used as a high country run, administered by after high rainfall in 1962. A proposal was Lands and Survey until the discovery of cobalt in developed by the then Bay of Plenty Catchment 1946. This began the intensification of farming Commission to ‘use Lake Rerewhakaaitu as a in the area with soldier settlement beginning in storage basin’. After a period of consultation 1952-53 and continuing until 1965. The develop- a decision was made to increase the size of the ment of forestry in the neighbouring Kaingaroa lake outlet into the Mangaharekeke Stream plateau began in the 1930s. Anecdotal evidence and lower the level of the lake. This work from farmers in the Rangitaiki Plains suggests was completed in 1967/68 with further works that the development of the Kaingaroa forest completed in 1974. Concurrent with these has had a moderating influence on the climate discussions was a proposal from the Conservator of eastern Bay of Plenty. of Wildlife, Department of Internal Affairs, to In the early years of soldier settlement the plant reserve land around the margins of the climate of the area was quite severe. This lake, principally with native vegetation. Some appears to be due to the exposure of the area native and exotic plantings of the lake margin particularly during winter months. Early settlers were completed in 1972. Other plantings have recall ‘the extremes of climate, the freezing been made subsequently but weeds are a temperatures and the “very hard frosts”.’ problem. The high incidence of weeds, particu- Planting shelter was a priority as was the intro- larly blackberry, around the lake margins is an duction of earthworms which were lacking in on-going issue. the soil (Rerewhakaaitu and Districts Reunion Climate was a challenge in early years. The Committee, 1993). exposure of the area and effects of high rainfall Localised flooding and erosion problems were events were the main challenges. There was a Lake Rerewhakaaitu Kindly provided by Environment Bay of Plenty. PAGE 118 • ADAPTING TO CLIMATE CHANGE IN EASTERN NZ Meso Adaptation Meso Adaptation ADAPTING TO CLIMATE CHANGE IN EASTERN NZ • PAGE major drought in 1967/68 with stock shifted out of the district. However, climate extremes don’t seem to have had as great an impact since the 1970s. Local farmers attribute this to increased topsoil depth and establishment of trees. There was also a general shift in New Zealand’s climate at the end of the Rerewhakaaitu Valley Kindly provided by Chris Sutton. 1970s, with the 1980s and 1990s 5. On-going monitoring of rainfall, lake levels characterised by a greater frequency of El Niño and aquatic plants is needed. events. There is evidence that our climate has shifted again, with increased potential for the Rerewhakaaitu farmers have been proactive high rainfall events that were experienced in the by initiating involvement in a Northland study 1960s and 1970s. on ‘Best Management in Pastoral Catchments of Shallow Lakes’ and the subsequent devel- Development of farming has occurred with a opment of ‘Project Rerewhakaaitu’ (http: deepening understanding by farmers of both //www.maf.govt.nz/sff/about-projects/pastoral- the potential and limitations of their environ- farming/).). BothBoth ofof thesethese projectsprojects areare aimedaimed ment, dominant features being the volcanic at identifying practical measures that can be soils they are working with and the presence of implemented to reduce impacts of farming on the lake. Progressive intensification has been a lake quality. feature over the last two decades, which has led to greater demand on water resources. Fluctuations in lake levels are clearly impor- tant, particularly in terms of maintaining water Current situation quality. The maximum lake level is less than it The biggest concern over the last decade has was before the development of farming as a related to water quality in the lake. This concern result of the work completed in the 1960s. The has arisen from intensification of dairy farming. more recent concern has been with low lake The Lake Rerewhakaaitu catchment is unique in levels rather than the high lake levels which the Rotorua Lakes area with a high percentage were a cause for concern in the past. While (nearly 80 percent) of the land in pasture. The there were lower rainfall extremes over the local community and Environment Bay of Plenty last 20 years, there is a possibility of higher (EBOP) have been proactive in working together rainfall extremes over the next two decades to address concerns over lake quality. EBOP have (see the Macro Changes chapter for information completed a benchmark study on the lake and on the 20-30 climate cycle known as the IPO). catchment (McIntosh et al., 2001). Key summary Fluctuations in lake levels are managed to a points are: degree. At present there is a weir that intercepts drainage from the south-east and directs it back 1. Large fluctuations in lake levels can impact to the lake when the lake is not overflowing. on water quality. However, if the lake filled and discharged over 2. Current land management is sufficient to the weir it would take the drainage with it. maintain lake quality. There is a dynamic relationship between the 3. Improved management techniques are immediate lake catchment and the Rangitaiki needed for the future to offset the poten- River, influenced by changes in rainfall and tial impacts of further intensification of groundwater. Water generally flows to farming. groundwater from the lake (White et. al., 2003) 4. There is potential for catchment protection with the implication that increased demand work, with conservation species, on public for groundwater could also impact on lake and private land. levels. There is some surface flow (via the PAGE • ADAPTING TO CLIMATE CHANGE IN EASTERN NZ Meso Adaptation Meso Adaptation ADAPTING TO CLIMATE CHANGE IN EASTERN NZ • PAGE 119 Mangaharekeke Stream when there is discharge view, but on the other hand less water to the from the lake) and groundwater flow (via the lake would, in theory, offset local obligations to Rangitaiki Ignimbrite Aquifer) to the Rangitaiki flood protection in the Rangitaiki Plains. River catchment. Some farms are in the surface Another important characteristic of catchment of Rerewhakaaitu but in the ground- Rerewhakaaitu is the very strong sense of water catchment of the Rangitaiki River. This community, developed through the pioneering physical connection to the Rangitaiki is reflected years in the 1950s and strengthened through to in the rating of Rerewhakaaitu farmers for flood the present. This provides a strong capacity to protection on the Rangitaiki Plains. proactively address issues, such as the work on The above information provides a difficult situ- lake quality, and to deal with times of stress, ation for local farmers and for the ongoing which may arise from climate extremes or other management of the lake. More water in the factors. lake is desirable from a water quality point of These maps show changes in average temperature and rainfall in the Rangitaiki River catchment for the October to March period.