The improved sentiment surrounding the outlook for China's demand for natural resources is being reflected by rising imports for some major commodities, but as usual it pays to be wary when interpreting the numbers.

Customs data released this week shows strong import growth in the first two months of the year in copper and crude oil, a more modest expansion in iron ore and a surge in imports of alumina and bauxite, the main raw materials used to make aluminum.

Taken at face value this lends support to the view that China is heading for a better spring season after a gloomy autumn and winter cast a pall over the outlook for demand in the world's largest consumer of commodities.

But it's worth delving into the numbers to work out if they are truly reflective of rising domestic demand for commodities, or whether other factors are at work, or indeed, whether it may be a combination of influences.

Take copper, for example. Customs data show refined copper imports jumped 27.6 percent to 652,474 tonnes in the first two months of 2016 over the same period last year.

That looks impressive, but it also seems that much of the gain has been driven by differences in Chinese domestic prices and those in the rest of the world.

Traders have been buying copper on the Shanghai Futures Exchange (ShFE) and selling on the London Metal Exchange (LME) on the view that the Chinese currency will continue to depreciate against the U.S. dollar, Barclays said in a March 21 report.

"This trade pushed ShFE copper prices higher relative to LME prices, to an extent that it became profitable to buy physical copper from LME, import to China, and deliver to ShFE," the report said.

"Physical traders reacted to this arbitrage signal by moving copper into China. A further piece of evidence for the ShFE-LME arbitrage argument is that ShFE deliverable stocks have reached all-time highs while LME stocks have declined to their lowest level since October 2014," Barclays said.

The Barclays view would mean that China's rising copper imports have less to do with actual demand for the industrial metal, and more to do with traders trying to lock in arbitrage profits.