Weather and (1989) 9: 7-13 7

A REVIEW OF TOPOCLIMATOLOGY IN

B. B. Rtzharris Department of Geography, University of , P.O. Box 56, , New Zealand

ABSTRACT Because New Zealand is such a hilly country it contains a wide range of topoclimates but these have received surprisingly little attention. Development of horticulture, continued hydroelectric power developments, irrigation planning, large industrial proposals, and investigations into local air pollution problems have stimulated interest in topoclimates. Studies which examine the spatial variation of climate by using the network of climate stations in New Zealand are reviewed, but it is concluded that these give only a general indication of topoclimates. Some papers attempt to fill in the gaps between climate stations with temporary special purpose measurements, or by finding relationships that allow mapping. The main topics discussed in the are local airflows, wind and shelter, growing degree days, effectiveness of various frost fighting techniques, measurement of vertical temperature structure of the boundary layer, and winter chill units. Unlike the case for other natural resources, such as soils, there is no systematic programme for the mapping of topoclimates at scales that might be useful to horticulture.

INTRODUCTION areas of the the climate is dis- This review first outlines the topography tinctly continental in character, despite the and climate of New Zealand and their control fact that they are no more than 130 km from on topoclimates, then notes an increasing in- the ocean. In addition, abrupt changes in to- terest in the topic. The few attempts to map pography, and the strength of the westerlies topoclimates are outlined, together with other ensure that many places are windy. studies on local climate and associated pro- In his review of New Zealand mountain cesses, although the latter survey is not ex- climate, Coulter (1967) notes "a rather large haustive. Finally, some ideas for the future average lapse rate of temperature with height are presented. and occasional periods of low temperatures in Because of their latitude between 34'S and summer" as being distinctive. Certainly the 47'S, the climate of the main islands of New juxtaposition of covered mountains and Zealand is determined by their intermediate snow free valleys produces large altitudinal position just south of the sub-tropical high contrasts in climate. The snow also generates pressure belt and on the northern fringe of the cold air drainage into the valleys and hemispheric westerlies. Other main factors intermontane basis where it is frequently that influence the climate are the country's trapped. For example, at Earnscleugh within position in the midst of a vast ocean and its an Otago intermontane basin, there are 180 shape and topography. The oceans ensure that ground frosts and 113 air frosts per year on there is abundant moisture for precipitation average, whereas on the eastern coast of the and equable temperatures. On the other hand, province at Dunedin, which is isolated from the mountains generate sharp contrasts in snow covered hills and where the maritime climate from west to east, and in some inland influence is strong, the number of ground 8 Topoclimatology in New Zealand frosts average 78 and air frosts just 10 per relocated because of the demands of alternat- year. ive land uses such as is caused by the en- The net effect of these factors is that there croachment of hydro lakes or urban areas. are at least 15 distinct macro-scale climate For example in , there was a regions in New Zealand. However, the topog- need to identify new orchard sites to replace those flooded by the Clyde high dam raphy creates a highly varied landscape so that a wide range of topoclimates are pro- (Fitzharris 1977a, 1977b, 1979, Beecroft et al., duced that can change rapidly over short 1983). There is also quickening interest in distances. The main controls on these finding new wine growing areas (e.g. Franklin 1968, 1969, Hutchinson 1969, Marris 1978, topoclimates are elevation, receipt of solar radiation, shelter from wind, distance from Milne 1978, Steans and Jackson 1978). In these circumstances, maps of local scale climate the ocean, and propensity for cold air ponding. have to be produced within a very short time, sometimes within a year. In addition, siting BACKGROUND TO MAPPING OF TOPOCIAMATES and construction of large industries lead to detailed investigations of likely air pollution The need for topoclimate maps in New dispersion and of the boundary layer in their Zealand is increasing because the pace of land vicinity, so that maps and statistics of use change is quickening. Historically, pasto- topoclimatic phenomena, such as the depth of ral agriculture has been the dominant land cold air ponding and inversion frequency, use and topoclimates were relatively unim- have often been produced. A summary by portant, because free-ranging livestock inte- topic area of the known papers published on grated any differences in grass production by topoclimates in New Zealand is given in Table grazing over the variety of terrain on the 1. farm. As a result, even agricultural research stations made little effort to identify topoclimates, although the measurements of TABLE 1: SUMMARY OF MAIN TOPIC AREAS IN THE Chiew (1976) and Tuckey (1976) at Invermay NEW ZEALAND LITERATURE ON TOPOCLIMATES near Dunedin, are notable exceptions, and Topic area Number of Papers some attempt to redress this deficiency is suggested in the guidelines of McAneney and 11 Kerr (1984). However, now that there is a Investigations for growing of grapes Investigations for growing of other crops 6 decline in the economic returns from grass- 9 land farming and a change to higher value Study of climate parameters (eg frost, wind) Study of alpine climate processes 8 crops based on horticulture, orchards and 8 vineyards, identification of the best Study of inversions, air pollution dispersion topoclimates becomes more critical because Investigations related to hydroelectric development 4 wise choices give large economic advantages to the grower. Total 46 Recent discussion of enhanced greenhouse warming brought about by an anthropogenic increase in the concentration of gases such as MAPPING OF TOPOCIAMATES carbon dioxide has raised the question of fu- Mapping of topoclimates should be at the ture for horticulture and other crops local scale, defined after Oke (1987), as areas (for example see Ministry for the Environ- between 0.1 and 100 sq km. In New Zealand ment 1988). Various scenarios have been pro- there are about 300 climate stations with posed, with the Royal Society of New Zealand longterm records, or one for every 850 sq km, (1988) suggesting a warming of up to 3°C. In so that although these stations record infor- climatic terms this is a large change that will mation that is useful for selection of horticul- greatly affect the geographical distribution of tural sites, the network is too coarse to crops. It is now realised that a sound know- identify local scale topoclimates. For exam- ledge of present topoclimates greatly helps in ple, in the fruit growing area of the "Central deducing future limits for crops in a green- Otago warm zone", which represents land house warmed New Zealand. highly suitable for production of export quali- From time to time orchards have to be ty stone fruit, there is only one climate station Topoelimatology in New Zealand 9 for every 2600 hectares. This is inadequate beause most orchards operate on less than ten hectares of land, often taking advantage of local climates in sheltered vales or on slopes where the risk of frost is diminished. 111. All criteria root Nevertheless, data from climate stations 2 Less suitable (rainfall <1200mm) have provided the starting point for 3 Marginal (GOD >900) topoclimatic mapping, and the New Zealand Meteorologial Service has produced a series of climatological maps at a scale of 1:2,000,000 which show the distribution of such things as climate regions, soil temperatures, air temperatures (several parameters), and rainfall (several parameters). Hurnard (1982) used the combined criteria of growing degree days, frosts, and rainfall, as recorded at cli- mate stations, to identify areas at the meso- scale that may be suitable for riesling grapes (Fig 1), although there were similar attempts as early as last century (Bragato 1895, 1906, Palmer 1898). Kerr et al. (1981) used data from 74 climate stations, 20 sunshine stations and 437 rainfall stations from the lower to begin the process of matching horti- cultural crops and climates. A sample of their results are shown in Fig 2. Normally growing Fig 1. Areas mapped by Hurnard (1982) as climatically degree days are accumulated for the warmest suitable for reisling white wine grapes. GDD is growing six months of the year (1 November to 30 degree days (base temperature 10°C) for October to April inclusive.

Napier Fig 2: Isolines of accumulated Apo° growing degree days above 10C for October-April inclu- sive which are exceeded in 8 out of 10 years. Area shown is the southern part of the North Island and is from Kerr et al (1981)

1000

Wellington • Climate station Land below 200m 10 Topoclimatology in New Zealand

April), and tables for various base tempera- tures have been prepared for 130 climate stations by the New Zealand Meteorological Service (1978). However, Jackson and Cherry (1988) do not favour the use of growing degree days and propose an index based on latitude and mean temperature of the warmest month. In order to calculate and map average de- gree days at the local scale, Turner and Fitzharris (1986) developed a technique which they illustrated with the example of the Ban- nockburn district, a 21 sq km area of diverse terrain in Central Otago. The following pro- cedure was proposed: (a) Obtain an accurate air temperature sen- Area Warm season sor and cheap screen to measure daily heat units 11111 A & B .1000 maximum and minimum temperatures. gum C 970 -1000 (b) Measure daily maximum and minimum OMNI 940 -970 temperatures at a large number of tempo- E 910 - 940 111101111 F & G 870 - 910 rary sites in the district of interest. The , 1111111111 H & I 800 - 870 sites should sample the main elements of 11111 J .‘800 the district's topography (at Bannockburn 45 sites were used). (c) Correlate maximum and minimum tem- peratures at each site with those recorded at a nearby climate station which has a long period of record. (d) Using covariance analysis, pool the subse- quent regression equations. This reduces the number of equations to those which Fig: 3. Distribution of warm season growing degree days are significantly different from each (or heat units) in the Bannockburn district of Central other. In this way groups of similar sites Otago (from Turner and Fitzharris 1986). are formed. (e) Use those pooled regression equations to can be deployed in a different district each generate mean monthly maximum and summer, so that a large region can be pro- minimum temperatures over the warm gressively mapped over a decade or so. Since season for each group of sites. the Bannockburn measurements were taken, (f) For each group of sites calculate warm the method has been applied::01)y both the season growing degree days (or heat units) Ministry of Works and Development and the from the monthly temperatures by using Ministry of Agriculture and Fisheries to the the method of Coulter (1974). Estimates Gibbston district in the Kawarau Valley, in are then made for a 30-year period. the Lower Clutha Valley from Beaumont to (g) Plot the results for each group of sites on Roxburgh, and in the Upper Clutha Valley a map, and extrapolate growing degree from Cromwell to Hawea. Similar techniques days to surrounding areas. are used in Northland to find sites for sub- tropical fruits, such as avocados, which re- The method provides maps of temperatures quire warm temperatures during spring and growing degree days (Fig 3, Table 2). It flowering. identifies those sites most suitable for horti- A further extension of these ideas intro- culture at a similar scale to other available duces the concept of the climatic quality of resource information, such as soil maps, and land. Just as other land resources are classi- can be used for land use planning and com- fied (eg first class soils), so also should cli- mercial decision making about further horti- mate. A classification which is based on both cultural development. A set of instruments warm season growing degree days and spring Topoclimatology in New Zealand 11

TABLE 2: ESTIMATED WARM SEASON GROWING DEGREE DAYS (BASE 10 C) AND PERCENTILES IN THE BANNOCKBURN DISTRICT FOR THE PERIOD 1949-80 Area A B C D E F Cromwell

Mean 1051 1017 987 969 921 905 894 841 833 669 981 min 832 800 765 753 701 686 682 626 618 468 750 10 919 887 854 838 789 772 764 711 702 548 843 20 955 922 891 874 826 810 799 748 738 581 882 30 995 962 930 913 863 849 840 786 776 615 922 40 1004 968 967 949 904 889 876 825 817 654 962 50 1030 998 967 949 904 889 876 825 817 654 962 60 1055 1019 988 970 923 904 895 845 831 669 983 70 1110 1077 1045 1029 982 967 953 903 894 723 1047 80 1161 1126 1095 1075 1028 1011 997 945 937 763 1092 90 1245 1201 1184 1162 1114 1099 1086 1030 1023 846 1186 max 1318 1281 1256 1231 1186 1171 1156 1103 1096 915 1259

Source: Turner and Fitzharris (1986)

frost has been used to assess the quality of statistics are given for 166 locations in land in the lower Clutha Valley (Table 3). The Goulter (1981), while a map of New Zealand, procedures are similar to those described showing winter chill unit accumulation is giv- above, with temperatures measured at a large en in McAneney and Kerr (1984). Local scale number of temporary stations. Spring frost mapping of fruit phenology is used to frequency is calculated using a linear regres- portray winter chill requirements in such sion relationship between incidence of air areas as the Bay of Plenty. frosts and mean monthly temperature. Inversions in New Zealand often represent the top of cold air pools that have drained katabatically off the surrounding mountains. TABLE 3: CRITERIA USED TO CLASSIFY THE CLI- Their climatology is therefore useful in MATIC QUALITY OF LAND topoclimatological mapping, as well as judg- Climate Parameter Classifi- ing the effectiveness of proposed wind frost- cation Name Criteria fighting machines, and has been assessed at specific sites using acoustic sounders, balloon Growing degree A High > 900 systems, instrumented towers or stacks, and days for the temperature differences between a valley period November • Moderate 800-900 floor and surrounding hills. At Upper Hutt to April inclusive (Wratt et al., 1984), South (de Lisle, (10 C base temp) • Low < 800 1966) and Motunui (Wratt and Holmes, 1984a), inversions occur for about 50 to 70% of winter < 1 and autumn nights. At exposed coastal sites, Number of days 1 Infrequent such as Aramoana (near Dunedin) and Tiwai with spring frosts 2 Some 1-10 Point (near ), their frequency is (period September- lower at between 20% and 30% (Bromley December) 1973, New Zealand Aluminium Smelters 1980, 3 Frequent > 10 Fitzharris et al., 1988). Winter night-time inversions at Motunui, Upper and (Thompson, 1973), Spring frost is a critical constraint to horti- Ohaaki (Wratt and Holmes, 1984b), and Christ- culture in most parts of New Zealand, and a church (Surridge 1979, 1980), begin to form few locations have been investigated closely near sunset and usually last until mid-morn- (e.g. see Probine 1949, Knox et al 1980). Frost ing, whereas at Aramoana the majority dissi-is 12 Topoclimatology in New Zealand

pate within 6 hours of formation. Average not used for horticulture, they need to be ground based inversion heights for all these formally mapped so that future planning can sites generally range between 100 m and protect them from land uses that do not capit- about 400 m. However at Cromwell, which is alise on this climatic resource. They should located in a large intermontane valley, they also have priority for new irrigation schemes are deeper and more persistent. In winter and when water is scarce or costly. Unfortunately, spring, inversions occur for more than 4070 of there is no agency formally charged with the time, with tops 180 to 500 m above the topoclimate mapping, although government surface (Fitzharris et al., 1983). They last for departments exist to map other natural re- much of the day and only break up for a few sources such as soils, geology and vegetation. hours in mid-afternoon. The New Zealand Meteorological Service are Local wind systems and katabatic flows developing techniques based on a combination have also been investigated in detail at some of topoclimate theory, field measurements, alpine sites (e.g. Sturman 1983, Sturman et al., and satellite infrared imagery (McGann 1988) 1985) and near the coast (Sturman and Tyson that may be valuable in the future for map- 1981, McKendry et al., 1987). Because of the ping climate in irregular terrain. Such tech- windy nature of New Zealand, much emphasis niques could well be combined with others is placed on shelter and several experiments that model spatial variations in surface ener- currently examine their influences on gy balance and airflow processes within a microclimate. geographic information system framework. CONCLUSION AND FUTURE NEEDS REFERENCES New Zealand is a country with a vast array Beecroft, F. G., Burton, J. and Fitzharris, B. B., 1983: of topoclimates. The density of climate sta- Survey and classification of land and climate for soil tions is not sufficient to categorise these so relocation and augmentation suitability for horticul- that they have not been mapped at the local tural crops, Lake Dunstan environs, Central Otago, New Zealand. DSIR Soil Bureau Report DN-13. scale except in a few localities where special 97pp+3 vols maps. dense networks of temporary stations have Bragato, R., 1985: Prospects of Viticulture in New Zea- been established. Most investigations of land. Government Printer, , N.Z. Bragato, R., 1906: Viticulture in New Zealand. Govern- topoclimate have been in reaction to a change ment Printer, Wellington, N.Z. in land use to higher value crops or in re- Bromley, A. M., 1973: Temperature inversions at Tiwai sponse to large hydroelectric or industrial Point 1972. NZ. Meteorological Service Report. developments. The main topics discussed are Chiew, W. Y., 1976: A study of the summer maximum and minimum air temperatures over rolling terrain at local airflows, wind and shelter, growing de- Invermay. Unpublished B.Sc(Hons) dissertation, De- gree days, effectiveness of various frost fight- partment of Geography. University of Otago. ing techniques, measurement of vertical Coulter, J. D., 1967: Mountain climate. Proceedings N.Z. temperature structure of the boundary layer, Ecological Society 14, 40-57. and winter chill units. Coulter, J. D., 1974: Note on the estimation of 'degree days'. NZ Journal of Science 14, 259-263. Effective mapping relies not only on a de Lisle, J. F., 1966: Temperature inversions over South Auckland. NZ Meteorological Service Technical Note dense network of measurement stations but 164. also on developing algorithms that allow in- Fitzharris, B. B., 1977a: A preliminary report on frost in terpolation and extrapolation of data across the Cromwell Gorge and likely effects on hydro the topography. Therefore studies that exam- schemes on its incidence. In Power Project, Environ- ine spatial variations in radiation and energy mental Impact Report on Design and Construction Proposals, Ministry of Works and Development, Ap- exchange on hill slopes and valleys such as pendix 14, 15pp. those of Greenland (1973), Greenland and Fitzharris, B. B., 1977b: Possible climatic effects result- Clothier (1974), Jackson (1967) and Radcliffe ing from the high DG3 dam at Clyde, as in Scheme F. and Lefever (1981) should be further In Power Project, Environmental Impact Report on Design and Construction Proposals, Ministry of Works encouraged. and Development, Appendix 15, 12pp. It has long been known that areas of New Fitzharris, B. B., 1979: Climatic questions arising from Clutha Valley development. NZ. Geographer 35, 64- Zealand have topoclimates that are very good 70. for the production of valuable export crops, Fitzharris, B. 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