Ari Venäläinen

Meteorological data for agricultural applications

Abstract Many agricultural applications are based on meteorological data. For example estimation of surface moisture, crop yield or forecasting of outbreak of crop diseases or insect pests is largely dependent on meteorological conditions. To ensure that there continuously is a (in spite of changes in meteorological observing network) spatially and temporally adequate amount of meteorological data available a system was taken into use in Finland, where parameters measured at observation stations are first interpolated onto a 10 km ×10 km grid. The data is stored as grid square values in a database and calculations are made using this gridded data. The spatial interpolation method currently used at the Finnish Meteorological Institute is known as kriging. The interpolated data has successfully been used in several agricultural applications.

Climate Change Promotes the Emergence of Serious Disease Outbreaks of Filarioid Nematodes

Filarioid parasites represent major health hazards with important medical, veterinary, and economic implications, and considerable potential to affect the everyday lives of tens of millions of people globally (World Health Organization, 2007). Scenarios for climate change vary latitudinally and regionally and involve direct and indirect linkages for increasing temperature and the dissemination, amplification, and invasiveness of vector-borne parasites. High latitude regions are especially influenced by global climate change and thus may be prone to altered associations and dynamics for complex host-pathogen assemblages and emergence of disease with cascading effects on ecosystem structure. Although the potential for substantial ecological perturbation has been identified, few empirical observations have emanated from systems across the Holarctic. Coincidental with decades of warming, and anomalies of high temperature and humidity in the sub-Arctic region of Fennoscandia, the mosquito-borne filarioid nematode Setaria tundra is now associated with emerging epidemic disease resulting in substantial morbidity and mortality for reindeer and moose. We describe a host-parasite system that involves reindeer, arthropods, and nematodes, which may contribute as a factor to ongoing declines documented for this ungulate species across northern ecosystems. We demonstrate that mean summer temperatures exceeding 14°C drive the emergence of disease due to S. tundra. An association between climate and emergence of filarioid parasites is a challenge to ecosystem services with direct effects on public health, sustainability of free-ranging and domestic ungulates, and ultimately food security for subsistence cultures at high latitudes.

Momentum and heat fluxes over lakes Tamnaren and Raksjo ¨ determined by the bulk-aerodynamic and eddy-correlation methods

Micrometeorological measurements made concurrently over two boreal lakes, Lake Tamnaren (surface area 37 km 2 , depth 2 m) and Lake Raksjo ¨ (1.5 km 2 , 4 m), during the NOPEX observational campaigns provided long-term latent and sensible heat fluxes determined with the bulk aerodynamic method. The turbulence transfer coefficients were verified with short-term eddy correlation runs over Lake Tamnaren. The drag coefficient and the Stanton number attained a stability dependence close to the Businger-Dyer form. During weak or moderate wind conditions, the latent heat flux determined from eddy correlation was close to that calculated with the bulk aerodynamic method using typical values of the Dalton number. However, the independent verification of the Dalton number under conditions of moderate or strong wind suffered from the poor performance of the fast-response hygrometer due to movement of the float. Measurements of the surface roughness suggested a value of the Charnock constant near 0.02. On average, the stratification of the surface layer over both lakes was unstable, but stable conditions occurred almost daily due to advection of warm air from adjacent land areas. High evaporation rates occurred even during stable stratification. The variation of the latent heat flux on an hourly or daily basis was strongly correlated with wind speed. This was also demonstrated by the higher rates of evaporation on the larger Lake Tamnaren compared to the sheltered Lake Raksjoduring strong wind conditions. Towards the end of the summer of 1995, the lake surface temperature attained somewhat higher values on Lake Raksjo ¨, attributable to its larger depth. This also resulted in higher daily average sensible and latent heat fluxes compared to Lake Tamnaren in August-September. Thus, in the long-term, the observed daily deviations between the lakes nearly compensated each other. # 1999 Elsevier Science B.V. All rights reserved.

The Influence of Climate Warming on Soil Frost on Snow-Free Surfaces in Finland

The influence of the predicted climate warming on soil frost conditions in Finland was studied using a climate scenario based on a Hadley Centre (U.K.) global ocean-atmosphere general circulation model (HadCM2) run. HadCM2 results were dynamically downscaled to the regional level using the regional climate model at the Rossby Centre (Sweden). The future period this study focuses on is the end of the 21st century. The study was limited to ground surface conditions in which snow has been removed. The predicted air temperature rise was interpreted in terms of changes in soil frost conditions using an empirical dependence that was found between measured soil frost depths and the sum of daily mean air temperatures calculated from the beginning of the freezing period. On average the annual maximum soil frost depth will decrease in southern and central Finland from the present approx. 100–150 cm by about 50 cm. In northern Finland the change will be from depths of about 200–300 cm to about 100–200 cm depending on station. The annual maximum soil frost depth in the future would thus be about the same in northern Finland as it is in the current climate in southern Finland. In southern Finland after about 100 years the ground will seldom be frozen in December and even in January there will be no soil frost in about half of the years. In Central and northern Finland the probability of completely unfrozen ground in December–March is very small, even in the future.

Comparison of latent and sensible heat fluxes over boreal lakes with concurrent fluxes over a forest: implications for regional averaging

The seasonal and diurnal variation of latent, and sensible, heat fluxes above two boreal-zone lakes and an adjacent coniferous forest was studied using data from the NOPEX field campaigns in 1994 and 1995. Heat fluxes over the lakes were estimated with the bulk aerodynamic method and those over the forest with the eddy-correlation method. The night-time latent heat flux, while non-existent from the forest, was significant from the lakes during all summer months. The day-time flux from the lakes peaked, on average, in the afternoon, while the maximum flux from the forest occurred around noon. The differences in the latent heat supply between the two surface types varied within(60‐80) W m ˇ2 , depending on the month and time of day. The monthly mean latent heat flux from the forest was higher than that from the lakes in May, in June and July the fluxes were about equal; and in August‐September, the lake values exceeded those of the forest. The sensible heat flux reached its maximum values over the forest near noon, but over the lakes during the early morning. An excess supply of heat over the forest of up to 200 W m ˇ2 was found in comparison with the lakes during the mid-day hours. From May to August, the monthly mean sensible heat flux was higher from the forest than from the lakes. The difference in the heat exchange of lakes and forest was also estimated based from airborne measurements made from an aircraft flying at a height of 100 m. For flight legs consisting of a 15% portion over the lake, the leg-averaged latent heat flux was, on average, 2% lower and the sensible heat flux 9% lower, compared to a flight leg over fully-forested terrain. # 1999 Elsevier Science B.V. All rights reserved.

Estimation of Surface Solar Global Radiation from NOAA AVHRR Data in High Latitudes

Abstract A physical method for estimating the instantaneous global irradiance and daily cumulative insolation based on Advanced Very High Resolution Radiometer data was developed and tested at high latitudes in a boreal subarctic region. The satellite estimates were compared with ground-based pyranometer measurements at six stations in Finland. From the comparison of instantaneous satellite estimates with 15-min average irradiances measured by pyranometers, a high correlation coefficient (0.97 in July 1996 and 0.99 in March 1997) between these estimates was obtained under clear-sky conditions. A standard error of 8% and a zero value of bias were obtained in both months. Under cloudy conditions the correlation coefficient in July 1996 was in the range of 0.79–0.83; in March 1997 it ranged from 0.89 to 0.96. The standard error in cloudy cases varied from 27% to 39% in July 1996 and from 17% to 33% in March 1997. For daily insolation estimates, the correlation coefficient had an average value of 0.95. The st...

Latent heat flux from small sheltered lakes

The dependency of the latent heat flux on the over-water fetch on lakes surrounded by tall, dense forest was studied by making use of measurements made on two different-sized lakes. The measurements were made during the NOPEX (Northern Hemisphere Climate-Processes Land Surface Experiment) field campaign. It was found that, in the case of a typical Scandinavian lake with a size of less than 10 km2, the latent heat flux will increase as a function of over-water fetch due to the increase of wind speed and in spite of the increased air humidity. This also has implications on area-averaged fluxes: when two lakes having similar shorelines, lake water temperatures and solar radiation conditions are compared, then the evaporation per unit area is smaller from the smaller lake. When the lakes are large, with fetches of several kilometres, then the significance of sheltering is small. If point measurements are used for the estimation of area-averaged latent heat fluxes from lakes with short fetches and forested shorelines then the distance of the measuring site from the shoreline should be taken into account, otherwise errors of tens of percent may occur.

The Finnish Forest Fire Index Calculation System

Since the summer of 1996, the forest fire index calculation in Finland has been based on surface moisture estimation. The calculation is done on a 10×10 km grid. Air temperature, air humidity, wind speed, solar radiation and precipitation measurements made at observing stations are interpolated onto the grid with an objective interpolation method known as ‘krig-ing’. Potential evaporation is calculated for each grid-square based on the interpolated meteorological data using the Penman-Monteith equation. The moisture of a 60 mm thick surface layer is estimated using potential evaporation and precipitation data and, finally, the surface moisture is scaled to forest-fire index values (1–6) which are distributed to the fire authorities through the Internet. In the future, the inclusion of weather radar and satellite information in the spatial analysing system will further improve spatial analyses of precipitation and solar radiation.

Effects of water temperature on year-class strengths and growth patterns of pikeperch (Sander lucioperca (L.)) in the brackish Baltic Sea

Pikeperch (Sander lucioperca), the studied species, is the most important amongst freshwater fish species, commercially, in the brackish Baltic Sea. We studied the effects of water temperature on three aspects of pikeperch growth in Haminanlahti bay, Finland. First, annual length increments were related to age and temperature using a non-linear growth model. Since length increments were based on back-calculated lengths, i.e. repeated measurements, the first order autoregressive covariance structure was used. The model showed that when temperature increased annual length increments also increased, whereas increased age reduced annual length increments. In the modelling, the best fit was found with water degree-days over 10°C. Second, the onset of growth of pikeperch in spring had a positive relationship with water temperature and a negative one with the length of pikeperch. The latter finding suggests that smaller, non-mature pikeperch starts to grow earlier than larger, mature pikeperch. Third, the year-class strength was positively correlated with water degree-days, and the year-class strength negatively affected annual length increments. This indicates that within a strong year-class subsequent growth is reduced more that within a weak year-class, suggesting density-dependent growth.

Seasonal soil moisture and drought occurrence in Europe in CMIP5 projections for the 21st century

Projections for near-surface soil moisture content in Europe for the 21st century were derived from simulations performed with 26 CMIP5 global climate models (GCMs). Two Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered. Unlike in previous research in general, projections were calculated separately for all four calendar seasons. To make the moisture contents simulated by the various GCMs commensurate, the moisture data were normalized by the corresponding local maxima found in the output of each individual GCM. A majority of the GCMs proved to perform satisfactorily in simulating the geographical distribution of recent soil moisture in the warm season, the spatial correlation with an satellite-derived estimate varying between 0.4 and 0.8. In southern Europe, long-term mean soil moisture is projected to decline substantially in all seasons. In summer and autumn, pronounced soil drying also afflicts western and central Europe. In northern Europe, drying mainly occurs in spring, in correspondence with an earlier melt of snow and soil frost. The spatial pattern of drying is qualitatively similar for both RCP scenarios, but weaker in magnitude under RCP4.5. In general, those GCMs that simulate the largest decreases in precipitation and increases in temperature and solar radiation tend to produce the most severe soil drying. Concurrently with the reduction of time-mean soil moisture, episodes with an anomalously low soil moisture, occurring once in 10 years in the recent past simulations, become far more common. In southern Europe by the late 21st century under RCP8.5, such events would be experienced about every second year.